I am almost certain that no, it will not be. The main point of buying one of these would be to use OpenCAPI 4.0 or NVLink 3.0, which would probably need a board redesign anyway.
NextPlatform wrote last year about POWER9’ potentially using OpenCAPI to interface with OpenCAPI memory as an alternative to POWER9 SU using SerDes to talk with Centaur-buffered memory; this is potentially further incompatibility with POWER9 SO&SU boards. You can read about OpenCAPI memory here:
Though I don’t really know all that much about these sockets. I never did get a reply about whether SO (Scale Out) and SU (Scale Up), even use the same physical sockets.
POWER8 vs POWER8’
From the RCS Wiki talk page on POWER8’ (listed there as POWER8E):
We have no direct experience with this module, aside from the fact that it does not work (or even fit) in the standard POWER8 socket.
Though that’s not a fair comparison, since POWER8 → POWER8’ added NVLink connections, whereas POWER9 → POWER9’ is only updating them.
There are a bunch of questions here,
- same physical socket?
- same electrical pin layout in socket?
- are NVLink/OpenCAPI backwards compatible protocols?
that I can’t begin to guess the answer to, but with this many unknowns, and little benefit to doing so, my guess is no.