If the various "redditish" projects could agree an shared framework providing access to all the features common across all implementations then sure, it'd be easy. But the thing is, that things are done just different enough that dedicated apps make sense to make use of any unique features.

Also, I've been using my phone's browser to post to kbin and I think it is fine.

I don't like the idea. But if it is going to happen it shouldn't be a bot alone, but an instance that only connects to reddit content, e.g it would virtually federate reddit as a virtual instance. That way people would need to explicitly subscribe to the subs otherwise you wouldn't see it at all.