A downside to the room service charge will likely mean people ordering more stuff than they otherwise would. "More bang for the buck" approach whether they planned to eat it all or not. So, more waste for Princess.
Royal Caribbean started the room service fee a few years ago, but only from midnight to 5am. Now I believe NCL is doing that too, or something similar. These things are often like price hikes at the airlines. One does it and the others fall in line. To Royal Caribbean's credit, they have not expanded the room service fee to 24/7 but it wouldn't surprise me if the did.
And while all of this is going on, the cruise line many love to bash - Carnival - still offers the closest thing to an 'all-inclusive' cruise among any of the mass market lines. No room service fees. A lot of alternative dining venues that are not extra-fee. No class structure on their ships, which is becoming more common with the suites being separated from everyone else as far as special treatment.