Yep, you've got the added problem that XMPP had: too many "MAY" pieces to the protocol and you wind up with a fragmented mess.

I don't think that's that big of a deal with nostr, but it is still a concern. The core parts of the protocol are standard, but if it isn't chess on nostr or some specific use case, you'll have different people using different clients that support subsets of the supported features and it ends in frustration. 

 I don't feel frustrated at all, when I see different clients I just feel joy.