For Warriors:

Robert Williams III at 28 y.o. is balling out this year, ranking in the top 5 to 10 among NBA centers in many categories (per 100 possessions), including OBPM and DBPM.

Duop Reath is another center that can fit in the Warriors but is being underutilized at Portland. He's a center shooting 41.8% from 3 and posting respectable rotation center rebound numbers at 7.5 per 100 possessions.

Thybulle when healthy is an elite defender and decent 3/D wing, and one can hope when he's back that he'd contribute well. But he's mostly here to make the numbers work for Golden State due to second apron nonsense.

For Portland:

Horford can serve as a rotation center and to help mentor their young centers in Clingan and Hansen, the latter of whom is currently losing development minutes behind Williams III.

Kuminga is the big target. Portland gets a super athletic and long young two-way player to bolster their rebuild under Tiago Splitter. Kuminga wants out of Golden State due to a rift with Kerr, but is clearly well-liked by the locker room and should find good success on a hot young Blazers roster looking to make noise in the play-in.

Gary Payton II returns to Portland, where he played in 2022-23. He would serve as a rotation guard and ball handler on a team that is currently depleted by injuries at that position, with Scoot Henderson, Blake Wesley, and Lillard all still out.

Overall:

Blazers might view Williams III as too valuable to their playoff chances to trade right now. But the potential upside of Kuminga if he gels in their system would probably be too good to pass up.

The Warriors might not feel this is good enough return for JK and expect some picks too, so perhaps Portland also adds picks.

Warriors might also not feel like this does enough to salvage the season after Butler's catastrophic injury. This trade does not try to address the open questions posed by Jimmy's ACL. I'm not sure if there even is a way to address it before the trade deadline but, assuming there is something else the Dubs can do to bring in a scoring wing, maybe Thybulle at least partially helps.