I've whiteboarded some very similar ideas to this! If multiple people are coming to similar conclusions, there might be something here.

In my thoughts, my hesitation is that I think I might have a bias for unit management, which is a new "thing" typical MMO players would need to start doing and optimizing in order to keep up.

So I wasnt convinced it would stick.

I think the new V Rising game has a well thought out and related mechanic along these lines in that you still have 1 character, but you can get "servants" which you send out on missions to collect / farm materials from areas you've surpassed