The thing is, RSS is about dissemination of content while follow/like/comment is more about dissemination of opinion. There were indeed some protocols to fill the missing pieces, including json-ld for having some sane, common format and the Salmon protocol to make information go back up to the source. Like a salmon. But it definitely was a patchwork of multiple technologies with various advancement status and quasi-inexistant documentation.

Today all of those are dead now in favor of ActivityPub. AP loses a lot of the simplicity that could make RSS ubiquitous (you need a home server and na application server to handle api calls) but the expected interactions are all there, and it's built to be extensible.

In fact, I think reusing the "everything is a file" is definitely cool and makes things easier to try, but you would definitely benefit from using the whole JSON-LD taxonomy. Things are already defined and have been used for some time in production, so you can expect some work has been thrown at it. It'd also make collaboration easier.