Gonna be real with ya, that's really farfetched. If Capcom was approached to have Jill as a character, Base game or otherwise, I'm 100% sure they would have obliged. Especially since the announcement could've coincided with R3make. What's more likely is that those talks just didn't happen.So don't know if anyone heard but there's some insider info regarding a rumor Jill Valentine was meant to be in Base roster until being pushed to DLC but Capcom wasn't happy with that and removed her entirely.
Could explain the RE spirits...
The spirits will remain an anomaly but it could've just been a marketing move by Capcom to get more fans interested in the series. Not a bad idea to do that in a game that's sold as well as Smash Ultimate has.