My hot take is that with today's conditioning, 4th liners shouldn't be playing much except in long games in the playoffs.
Do you need one or two spare forwards to fill in for shifts where there is an injury, or a player is in the penalty box? Sure. But do you need the 10th, 11th, and 12th best forwards on your team skating a regular shift all together? I'm not sure.
I get that this allows teams to 'stretch' forwards ice time on the PP, but we're gonna have two decently balanced PP units if they play their cards right.
If they up the ES minutes of (Now possibly third line players) Chytil, Kredier, and the like, we shouldn't have to see Lemieux at ES more than 9 minutes a game and the other two guys more than 5. (Though ideally they can kill penalties.)