I don't want anymore power up characters.. I honestly dislike the idea of multiple variations, so even Dry Bowser annoys me more than most. Pink Gold Peach and Baby Rosalina instead of Diddy Kong or Bowser Jr. was a pretty harsh blow, especially when the DLC rolled around Tanooki Mario, Cat Peach, and Dry Bowser came back. Dry Bowser shows that they can bring veterans back, so why not Diddy Kong or Bowser Jr? Also would've preferred Excitebiker reimagined and the actual Captain Falcon.
That said, if we had to have a power up character, I would gladly take Cat Rosalina over Metal Mario, Pink Gold Peach, Dry Bowser, Tanooki Mario, Cat Peach, and all of the babies combined. Rosalina is one of my favorite characters and I liked the cat suit in 3D World, plus the color references were great (although I do believe that Mario should've had the Black Cat Suit [Galaxy Red Star bias], Blue Toad should've been Yellow Toad with the Yellow Cat Suit, and Rosalina should've received the Blue Cat Suit to fit the characters better while keeping the cultural tie).
Personally, I just think stuff like Power Up characters should be alt costumes like the Yoshis and Shy Guys, though the different animations they give them may be why that doesn't happen.
Dry Bowser, however, is debate-ably a different character to Bowser. In some games, he is just Bowser's skeleton. In others, he is a separate entity altogether (e.g the Adventure Tours mode of Mario & Sonic at the Winter Olympic Games, on DS).
I think Tanooki Mario and Cat Peach should have been Kitsune Luigi and Cat Rosalina instead. If they had to make variations of existing characters for DLC, they could have done it for someone other than Mario and Peach, since those two already have 3 versions without the DLC. I can understand why they went with Mario and Peach though - Tanooki Mario is more iconic than Kitsune Luigi, and making Peach a cat probably seems more immediately appropriate since she is supposed to be the cute, innocent girl. Cat Rosalina probably would have been received much better though, because a lot of people like her specifically in 3D World (there is just something funny about a cosmic deity walking around in a cat onesie and making accurate cat impressions - plus, a lot of people like the black colour most, for some reason), and because Rosalina, prior to this DLC, was the most used character online by far. The latter point may change now though, since Link is in the same weight class as her and is just as entertaining to play as, and is the most fresh addition to this game's roster in general.
As for the Cat Suit colours in 3D World, well that's getting a bit off topic, but according to the Iwata Asks interview for 3D World, Rosalina probably was going to have a Blue Cat Suit, but a special request was put in by one of the game's lead staff for Rosalina to have a black one. While the definitive answer is unknown, this video provides a solid theory as to why (and I'd wager you've seen this):