For the premium costumes, I think Capcom may have gotten some idea from Namco. For Tekken 7 the past year and till now until FR in a couple of weeks (since Namco is overhauling the customization on Tekken-net due to player complaints and suggestions), to buy the premium customizations, I say customizations and not just costumes (some costumes are split up into seqments for example while others are whole outfits), it would cost about 300 Banacoins or ¥324 yen each. So while Lili's gothic Lolita dress is one complete outfit, for Lars to get his unique street wear and visor that's actually three separate parts (upper body, lower body, glasses). Also you cannot simply select these for purchase, you are actually randomized lotto tickets for said items. Just to give some perspective on the matter from the Tekken side of things.
And unless these items are added into the rotation, they still as premium items and some are seasonal only premium items too.
For example, unless they decide to bring them back, if you didn't get the premium idol master stuff for the ladies, then you missed out period.