It's... I mean, I can understand why they wouldn't want the same basic costume appearing three times, which would crowd the composition amongst other things. But it gives a lot more weight to the Flashattan look than it essentially deserves. (It's maybe best seen as "post-Rebirth Wally" than "Wally through the ages"?)
[This apparent confirmation also leaves open the question of what Barry's going to be wearing. Because if Barry keeps his standard costume, they're going to be nigh-indistinguishable in any sort of crowd scene.]