I don't get why the big clubs are pushing for it to be honest, they have the squads.
I've seen Duffy tweet in support of it from an injuries angle, and Blades Analytic tweet about it, and yeah I don't want any players to get injured, but a) you shouldn't change the rules in the middle of a season, and b) the managers should just play someone else.
It's not meant to be easy to be top of the league, in the cups and playing in Europe.
If Pep can't play Aguero every week, play Jesus, or Torres, or Sterling etc. Pretty much all the clubs outside us, West Brom, Burnley, Fulham, Leeds (and possibly Palace and Villa but I think they're a bit better off than the 5 I listed) have enough quality to take 5 players out of their best XI and still have a chance to win games, especially in the top 6.
If they want to be able to take them off, why don't they just not play them if they're concerned about their fitness? Instead of trying to have their cake and eat it by being successful and having it made easier to remain so.
It would be a better league for having a bit more variety and opportunities for the inexperienced/younger players and fringe players to get games at every club.