who is going to pay the players in this new league? If this was something they wanted to do they could try to go to a league that already exists like the XFL and make $50,000. And if they are under contract with an NFL team things would be dicey legally to say the least.
This was already done in the past with the USFL. Jim Kelly, Steve Young, lots of big names played there for a bit but not many % wise and the NFL did just fine.
The idea that the top players would all decide to leave the NFL and take a massive paycut so that some unproven rookie can get part ownership of an NFL team (but they're leaving?) is just goofy.
What would happen IF a bunch of big name guys left is other NFL players would see opportunity for starting jobs and more $$ in the big league. You think Mahomes is walking away from a half billion dollars to make peanuts in some spring league?
There is 0% chance any player is getting part ownership of a team, especially an unproven rookie. He will get tens of millions of dollars per year though, mostly guaranteed.