Ok. Maybe not in the form of an express carrier flying under the flag of mainline - but there would be other low paying pilot positions at other types of companies hoping to attract pilots looking to build time.

What you said was this:
What possible reason would those airlines have to do that? Because those 250 hour wonders deserve a spot at the bigs without actually having any experience? Airlines with a choice are under no obligation to provide OJT to underqualified pilots. I think perhaps an attitude like yours is product of some strange times at the regionals and somehow you have decided real flying experience is optional. It just so happens that when regional operators were allowed to hire 250 hour pilots and they were hurting for candidates, many were able to bypass any real experience and get in the door. That doesn't necessarily make that path a recipe for success.

The simple fact is that driven pilots who really want a job at a major airline will always find a way to get the quals. There just aren't that many major airline jobs available during any given year to require lowering standards in the USA. We'll always have qualified pilots to fill them. Attempting to come up with an unlikely scenario that would suddenly require majors to hire 250 hour pilots is a waste of time. They won't do it because it's a bad idea and they don't need to.