In the original CRISIS, the skies of each world on the verge of being destroyed turned reddish.
The mention in this series of a coming "crisis" and red skies is a nod to that. There's nobody here who can tell you what the show runners have planned in the way of other DC characters being involved if we get to the point of seeing the "crisis". There's also no way of knowing the full extent of the coming "crisis".
Wells did say that his experiment made the barriers between their universe and other universes thin, and even punctured them. It's possible there's more coming as a result of that. Similar "crisis" but for different reasons.
That's just a guess.
The history that Wells knows says that Barry vanishes during the "crisis", likely dead. It could be the end of the series, and the opening of a door to Wally taking his place.
I don't think any of us want to see the "crisis" happen any time soon.
I forget if there was any indication in the news headline Wells looked at that suggested how far down the road the coming "crisis" is.
I beleive the headlines showed the year was 2024