They actually did that with Inca for awhile and it was pretty awkward.
I don’t think it’s quite the same in the case of revolutions. Having a revolution mechanic but omitting one of the earliest and most impactful revolution in history seems like a bad way to go. Having them both as a revolution and full civ is for sure awkward but that’s only because USA and Mexico are a very poor fit for full civs.
If they would have put the effort that went into USA and Mexico into fleshing out the revolutions they would have had a much better and more consistent result. Just allowing Spain and Britain to revolt earlier and then age up with states or revolt again would have been much better. A full range of state age ups could be achieved by having different states available to different starting civs (Dutch having access to New York, Michigan, and New Jersey, Sweden having access to New York and Minnesota, British having access to Virginia, Massachusetts, etc).