I'm hoping there will be some nice ITX B550 boards with 3 or more phase SoC VRMs with some decent power phases. Or just two doubled ones I guess. You don't need fancy cooling if the load is spread across more hardware after all.
As for frequencies, I think 2.5GHz sounds way too optimistic. Even if this ships at 2.1, that's a really, really high clock for a GPU, and hitting 2.5 would be borderline miraculous. 2.3 sounds likely as an OC if they ship at 2.1 though.
Also, for those of you trying to compare FLOPS and such, remember that this will carry over the decoupled Fclock of mobile Renoir, so it should be able to run DDR4->4000 if you are willing to pay for it or spend some hours tweaking some E-die. That would be a significant boost over 3200 on Picasso (yes, I've seen people hit 3400 on those, but it's rare and rarely stable over time).