Requiring an ATP to sit in a part 121 air carrier seat will single handedly solve the puppy mills pumping out 250 hour wonders and Multi Pilot Licenses.

And lower the available applicants for part 121 jobs, possibly raising the entry level income (but I doubt any raises beyond that).

However, imagine how competitive those jobs that bridge the gap between a wet 250 hour commercial license and a wet 1500 hour ATP will be. I predict that there will be MORE pay to play and abuses of people who just want to fly.