Well, it’s not the first time. According to the SE history, the third iteration did not have any costume either.
Placeholder? I don’t think so. Doesn’t look like any of all the placeholder SE lists I have seen but never shared.
Could SGG change it at the last minute? Surely they can just like any balance update. As @Zakuha said, we are just the messenger and we share what we see right now. It’s up to SGG to stick to it or change it beforehand.
Haha thank you 
Keep in mind, as discussed above, that SGG has an history of postponing a bit every covenant summons than initially planned. The actual portal’s rosters are rather stable on the other hand.