I mean it's possible? Then again they still have faction-based skin lines, like commando or crimson elite. I'd say it's a really stupid move if they go and do that, I don't see why they would; this is established lore within a faction, which is something they've stated they want to explore more of; that's one of their reasons why they retconned the league in the first place (not saying the reason is good or bad, just saying that's what i've heard from them. Sorry if I come across a bit...snappy. I'm so sick of lore retcon discussions). They don't retcon lore randomly or on a whim, they have some sort of directedness in it (again, you can argue about the validity of all that or whatever, I really don't care)
Don't worry, I've had enough of retcon's discussions myself, so I perfectly understand xD
Nevertheless, the problem with a retcon, in general, is just this: done once for something (in this case for the very thing that gave the game its name), they could conceptually do it for anything. In this case, given how huge the retcon they pulled out was, this would come as really a minor thing too, with respect to the IoW erasure.
You are right saying this wouldn't make sense with their stated intentions, but I do not trust them enough to adhere to those strictly. The reason being that they stated they wanted to preserve the core of retconned characters, but I've seen a very different Xerath's background story. Also, I've seen narrative say that champions were summoner's puppets, which is against their very own old lore, as explained in some JoJ issues.
I don't want to argue about this two latter points as to why I don't trust them, I just wanted to expose why it wouldn't come as a surprise to me if things were this way. I perfectly understand some people may disagree on the "not changing champions' core" thing or the other example, no need to argue back if you're tired of this kind of discussion, you can just tell me you don't agree and I'll understand =P
bloodmoon seems like a cool ionian bit of culture that they'd want to keep. it's like them getting rid of the solari or something, it's just weird and random, pretty much completely counters what they were trying to do with the retcon in the first place (explore the other areas of runeterra).
I agree it would be pretty arbitrary, but what has been not in the retcon? I could argue
EDIT: well, I have my lore a bit backwards, bloodmoon is a show put on after the noxus-ionian war, but it tells a traditional story. Not sure if the costumes were also traditional, but how it worked in my mind is that Kalista is an ancient Ionian warrior that was betrayed, but she had something to do either with the original story bloodmoon is based off of, or she performed it herself many years ago.
EDIT2: new announcement has an Ionian fleet sinking due to the harrowing 33 years ago (I'm assuming that's how it works), I would guess this is where Kalista comes from.
It could be, but I can't see her as Ionian in her design, plus if it was so her betrayer would probably be an npc.
Besides, she has a quote saying she remembers the Shadow Isles and another one for "this land was once so beautiful" (or something like that) that, if I'm not mistaken, is something the altar on Twisted Treeline says too.
Also, she makes references to the Ruined King: why would she if she was a Ionian caught by an already existing Black Mist, which is probably the result of things going horribly wrong in the Shadow Isles?