Farmers would probably leave the game. There is no reason for the rest of us to leave.
It's a misconception that lower league teams need a lvl 6-7 trainer. I never used lvl 6 until I was in DI, and never used lvl 5 until I was in D2.
They are too expensive for lower league teams, and have high salary.
It would certainly mean less world-class 140+ tsp players on the market, which would mean that D1/BBB teams would actually have to train their own world-class players, and not wait for the farm teams to train for them.
And it would increase the number of 110-130 tsp players, which would help D2 & D3 teams.