OKC has a guy that's not that much of a step down from Drummond. Why sacrifice something to have a slight upgrade for a guy who's the same age? Unless Detroit takes Paul and offloads some assets back, no point for OKC.

Boston makes sense but the Pistons don't want to take on salary. They want cap relief and draft picks. Boston can offer picks. And in your example, Hayward works because he has a player option this summer. If he doesn't want to stay in Detroit (he won't) he can opt out and become an unrestricted FA.

He'd be fun on the Hawks or Warriors too. Dallas might be a front runner. They need a C too. Clippers might be a dark horse. Would have to find salary to match his $27 mil which would gut their depth. But Harkless ($11M), Patterson ($2M), Green ($4.7M) and Zubac ($6.5M) could get them close. The problem would be losing their bigs depth.
Also Harrell is gonna get a big raise this summer so they'd be limited going forward. Drummond is durable but they'd still need guys behind him. Maybe bring in Noah? Or some other washed big back up? Their young players probably aren't ready yet.

Pat Bev, PG, Kawhi, Harrell and Drummond would be a devastating defensive group though.