Everybody is doing this. I don't see why SNKP shouldn't do that. Anyway, alternate outfits are something optional and don't affect the game at all, so they can be ignored.
What I don't like are DLC chars, because do not buy new characters is quite hard because, even if you don't like them or don't want to use them, you will fight them, so you need to know them. Like Yoda in SC4. I totally hate it was DLC, because he was a very tricky char and I never could practice against him to know him well because I didn't want to buy him. So, when I found some Yoda online I never knew how to attack him or cover from his attacks. Grrr.
On a side note. Alternate outfits could be great, not only because are something cool in terms of visuality, but also because it would be the first time someone do alternate outfits in a 2D game. This could give to SNKP a very good feedback. I really would love an "alternate outfit" for each character like the ones Yuri, Raiden, Andy, etc. have. But don't forget that do this for a 2D game is a titanic work (all frames have to be duplicated and redrawed, and each character has around 500-700 frames...).