Where the economics work someone will find a way.
Whoever said you needed codeshare? I can picture someone putting together an online portal - something like Amazon - where you just place an online order for a Moxy-like trip from city x to city y, and depending on sales, someone flys you on an MRJ or A220 or whatever aircraft makes the most economic sense.
Even legacy airlines are not immune to economic reality. Just ask TWA and Pan Am. Yes, it would require a hellacious amount of startup capital, but there is more of that concentrated in fewer hands than ever before. When we have people talking about space tourism and private companies putting people on the moon, a new regional/major without scope limits is not outside the realm of possibility.