They can start an entire new saga with the X-Men as the foundation. They don’t have to use them in this universe. They could Have new actors play Elseworlds versions of old characters (like how Falcon took on the Cap name). Hell, you can used RDJ as a Batman Beyond type role here and there. A reset isn’t exactly a reboot.
Why would the mcu x men not be in the main mcu universe to start with?