@hrefna
I like the idea of a simple base protocol with extensions too. My main worry is fragmentation of support for extensions. This could be avoided somewhat if one can define some kind of bundle of extensions as an optional standard. Something like "foosocial.com 2.3 requires: Follows 2.0+, Likes 1.1+, Boost 3.0+, ...". Then sites could negotiate with those standards rather than trying to negotiate some common subset.
Unfortunately, I think Nostr has too bad a reputation from its users.