i want good confidential compute for cases where e2ee is impractical, like an email server or immich with server-side ml/processing etc

Who are you protecting data access from in those cases? My suggestion was that it's probably more practical to run those kinds of solutions on a hardware stack you trust; in our basement or in a small box on the wall in your living room.

Besides, the specific extension we're talking about protect registers and computation and not shared memory.