I don't care how big the roster could rise to, 18 games is too much. For Superbowl teams that would mean as much as 22 games in one season.... nearly twice the college season!!
With all the emphasis on player health, that isn't going to happen. McVay has already taken the drastic step of refusing to play the known starters even for a series at any point in the preseason. He gets it that even 16 games is severe.
I can see a minor roster adjustment to perhaps 55 players and 48 on game day. Basically, since these are end of roster players being added, then we're looking at the minimum wage players. So the cost to the team in salary might be a total of $1mil. This would allow teams to keep development players without exposing them to waivers. This would necessarily mean keeping the PS players to 10 in order to make the Union happy.