I was born and raised in Orlando, live in Orlando to this very day.
I remember when DL had a hub at MCO, I remember when they abandoned it and yes they have sort of brought parts of it back over the years, but selectively.
DL is king at MCO, between DL, VA, LA and now AF, that is a lot of seats, I just don't see UA making a play here.
Plus, MCO can be very price sensitive, yes there is big business here, but compared to the vacation traffic it is tiny.
UA would be smart to maybe do some more point to point, but a full fledged hub, UA would be better served elsewhere.