I just think it makes DC's integrity seem a little flimsy. They took the leap with the New 52 and redesigned all of their core players, putting Superman in a suit of armour with a collar and dropping the super-undies. It was a bold move not many people loved and they refused to backpedal on it... for a while. They partway bring the outfit into the Superman movie but don't go the whole way. They continue to release cartoons with the old style because they're more relatable.
It's not that I want one outfit or another*, I'm just reminded of Xbox One having all those daring new ideas and then chickening out because of the public's confusion.
That said, this Supergirl outfit just looks exactly like the one from the 80s movie, albeit with a "modern" texture à la Spidey 00s/Superman Returns. It's more than a throwback, she looks like a cheerleader.