I just think the costs are going to get to a point where the non-professional programs either need a way to contain their costs or start dropping programs. In theory FCS is meant to cut costs associated with running a football program, though back when it was devised (I could be wrong here) the main cost was scholarships. Not the arms race for facilities, coaching salaries, various non-coaching staffs that support the programs, etc. that we have today.
That said, such a merger would require a rethink to how FCS is approached, with mechanisms in place to contain the runaway NIL train. I can't pretend to know what the answers are, but I am fully convinced the real divide soon will be between the well-funded NIL programs and those that aren't regardless of FCS or FBS classification.