I'll be damned - apparently 40nm retrofits ARE a thing, but I'm not clear if they are official or not. Here's a thread kicked off with an example found in the wild, bought from Japan. Note the discussion of resistor replacements:
https://www.psx-place.com/threads/frank ... 69/page-19I haven't read this all so I don't know whether they are official or not.
It sounds like they have the resources you need. They're talking about software issues in the last pages, and apparently they can be worked through.
Reddit says CECHA models serviced from 2011 got the updated slim (40nm, I guess) GPU:
https://www.reddit.com/r/PS3/comments/l ... &context=3