All of this is addressed in the article. The protocol doesn’t address this stuff because it’s meaningless in the context of the protocol. If you want the extra features then there are other protocols and social networks.

Also if you wanted a .plan for different people you would code your own server as in the article and tie it to a different “user”. The original server ties .plan files to username home dirs but there’s nothing stopping you from changing how that effectively works on your own server.