you sound like you're trying to write The Handbook on How To Have a Successful Rap Career on Independent or Major Labels and Gain Long Term Recognition. that's a herculean task, probably not even possible (every career is unique), maybe not even worthwhile (what would be the aim/outcome? to scientifically explain why 2Pac or Eminem is the most successful of all time?)

you listed 5 forces
rapper; beat; media outlet; industry; audience
and said they're all just as important to 'the sound of rapping'

but
- one guy beatboxing, one guy rapping, is that not hiphop?
- solo track recorded in home studio - is that not rapping?
- freestylers who don't get to choose their beats - are they not rappers?
- park jams before any media coverage or industry existed - was that not hiphop?

i mean i can see how these outside factors would have to be considered if we were analyzing the careers of say, (hollywood) movie directors. a movie is such a massive project, it requires millions of dollars funding, and numerous other pressures that need to be managed. but the fact is hiphop can be made in a bedroom. the 'context' is not necesarily operative on that grand level. when you read an article on hiphop drum programming techniques you don't expect it to be blown up to macrocosmic proportions, you expect it to focus on a narrow musical jurisdiction; at least part of the rapping is similar to this

talking to rappers would probably be instructive. but
1. not easy to do (i mean, hard to contact)
2. just because someone does something doesn't mean they fully understand it or even realize it. we're all english speakers but how many people really understand the inner workings of the language, or the pronunciations they're using, or the rhythm of their speech (eg. ppl think they leave pauses between words when speaking - they don't). a rapper might say 'patterns? fukchu talking about?' but the fact they're writing in lines means they're already using patterns (assuming they fit one line to one bar)

as for the excell spreadsheet of rappers, it would be ideal, but maybe not feasible
it's like can you grab a book and say 'how well did the author make use of adjectives, one to ten?' you can't give a hard and fast answer, yet you can instantly recognize whenever they use an adjective. or rappers might do one thing very well, but the flaw is their overall repetitiveness, using the same pattern every song (Cube). still, above we were talking about Eminem's The Way I Am for instance.

now, before going on, these two things:
this bit
"Second, and more importantly, you’re either not thinking hard about it, or you trying to push your “lazy rhyming” agenda with in post that should be neutral. (dictionaries try to be neutral) "
i think you're overreacting.
'seeming lazy' is NEVER good, by definition
this 'lazy rhyming' thing wasn't my agenda about MCs who use tired rhymes
it's about the accuracy of the rhyme. the concept gives a lot of scope for being lazy, like if it gets to the stage where you're ending lines with 'seen/lane/dating' and acting like it rhymes, and the listener notices. course they might not notice, you might have such a dope line they're distracted. that's why i wrote SEEMS.

and this:
"It goes without saying that I disagree with your conclusion that changes in ‘pacing’ create a feeling of aloofness."
ok i didn't mean aloof in an emotive way, i was just using an elaborate word to describe something technical. like saying 'Schumacher seems aloof from the standard breaking points as he speeds round the race circuit.' the listener SENSES an detachment in the rapper's rhythm; like how they SENSE speed if the rapper switches to doubletime, or if they use accelerando. that much is hard to argue with. i then went on to say how this COULD be used in an emotive way, which is just my judgement -- although there is frequently general consensus about this sort of thing, i was reading a jazz forum and they ALL seemed to say playing behind the beat creates a 'laid-back' groove, which is emotive.

sidenote:
"That idea, “if I the rapper do X, the listener will feel Y” is beyond problematic. That may be a common sort of analysis in poetry, but it has no place in rap music. Honestly I’m not sure how English/Literature/Poetry people can discuss anything substantively when they go back and forth with that kind squishy reasoning, but as a matter of policy, we shouldn’t be importing bankrupt concepts like that into rap analysis. "

(well i think it's because they've reached a nexus of understanding, with their peers, that allows them to grapple with concepts at the edge of mutability. i mean these people are incredibly well read, most folk don't even touch poetry or even literature. also, in music you have things like a change to a minor key creates a sad feeling - universally recognised, within western culture at least. what's to say poetry can't have the same sort of mechanisms)

moving on

rapper interacts with the beat
yes
i didn't mention the beat much
BUT, you could basically tack 'in relation to the beat' onto everything i listed
like patterns, you might want to leave a gap at the end of your line to make way for some sound element in the track (like the 'ONE' in that supreme clientele song at the end of every loop)
or pause so that each line starts at the same time as some riff in the beat, like the emphatic bass in Gangstarr's 'Take It Personal'.
or make your pattern the same as the drum pattern
and all the different cadences you could do to match something in the beat, or the energy to suit the music (like Nas's low key delivery) on Still Dreaming). etc etc. i'm wary of talking about 'the beat' like hiphoppers do so often cause it's still a musical entity, or rather a collection of musical entities which the rapping must coexist with.

('course a capella is still rapping, also didn't 2Pac start to just rap over drum machines or metronomes and leave it for his producers to fit a beat onto)

the things you listed
- change in voice, impressions, impersonations
* those are fine but i think they're more specialized things, they're advanced, rare. i was going for the basics.

- voice: deep, nasally etc
*post 28, agreed this should have been on the list

- punch ins, studio magic
*relevant to rappers when recording, but relevant to the audience when they hear the final product?

- breath control, long flows without pausing
* the former i feel is outside the final product, it's like talking about how able a screen actor is to complete a scene in one take. long flows i'd put under patterns. of course in a LIVE setting, it all merges (as it would for stage actors)

- mood, tone, emotion, energy, smug, preaching, boasting, crying, angry (why stop there though? could go on, 'loving, comedic, calculating...')
* i think there's distinct things going on here. 1. lyrical ability to construct a mood or tone or emotion (even energy arguably... rhyming about propane or something). 2. ability to express this in your voice. some rappers write emotive stories then deliver them like any other rap, some try to make their voice itself sound pained or whatever and just end up sounding whiny. --- but also, a little emotional colouring could be required just for a few words in an otherwise straight forward rap. that's why i put this under 'intonation' or something. Monch's Trilogy track i think is a supreme example of applying these little touches)

- speed
* again under patterns IMO. cause they are bound to stick to the tempo of the track, so then the 'speed' is a matter of how many words per bar/line they use, which is a matter of patterns. ABILITY to fit loads of words in i think was covered under 'enunciation'

- rhyme scheme, rhyme pattern
* i suppose you could have them separate

- harmony
* in what sense? literally when they sing a chorus together?

- references, poetical devices, mimesis
* see i think these things are separate from the sound. they can all occur on paper. they would add nothing to the listening of someone who doesn't know the language or can't make out the words (in a club with a bad system for instance). in what way do they interact with the sound, even, except that they are said?

i tried to list the the 'prime numbers' the things that couldn't be broken down much more without getting extra complicated, so perhaps that;'s why you don't think they interact. also i agree it's best to stay neutral... but this is okp, you've got to give something to bite. also, in the words of Casual, this is just SOME of the stuff you need if you want to be raw. the reason i opened with the 'beats and rhymes' statement was to point out how the sound aspect of rapping is overlooked. rapping - lyrics = sound

p.s. i think a useful question to ask is, if you took a classic rap, got the instrumental and gave the lyrics to someone who had never encountered it before, told them to record it, why is their version not going to be very good?

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Why do you choose to mimic these wack MCs?
Why do you choose to listen to R&B?

"There are obviously many things which we do not understand, and may never be able to." Leela

*puts emceeing in a box*