I'm the maintainer of parso. Feel free to addd me to the Nosy List if we have these discussions in the future.

Parso is indeed a lib2to3 fork with error recovery, round tripping and incremental parsing as its features. Most pgen2 code has been rewritten since for various reasons, but it's essentially still LL(1). We're currently trying to think how to proceed with Non-LL(1). For very simple cases a few hacks could suffice, but for larger stuff we will probably need to implement some form of PEG parsing.

I'm mostly worried about incremental parsing breaking if we replace the PEG parser, not about writing the PEG parser. But I guess we'll find a way, because I don't want to abandon Jedi (which depends on parso).