An updated document would be clearer and easier to understand. Developers wouldn't have to go back and forth between the document and the ERRATA.
It would not have new features. Those happen in the Community Group, or in FEPs, which, again, anyone can join.
If you oppose forming a working group, that means you oppose having an updated document, and it means you want things to be harder for developers, so we have less software and less fediverse.
Maybe you shouldn't oppose that.