If it results in larger rosters then that's more jobs for players, which would likely get NFLPA support.
The two additional meaningful games means they can bleed the cash cow TV networks even further. This grows the whole pie, including the players' part since they get a percentage.
This would allow teams a built in avenue to rest hurting players and would really give a a greater advantage to teams with better player acquisition skills. Deeper rosters talent-wise will matter even more. This isn't as bad an idea as it sounds at first glance. Especially if there are some built in exemptions for K, P, LS and even QB.