Well, I'm frigging nostradamus
Smallville's Lois and Clark Reunite! Erica Durance Joins Tom Welling in Arrowverse 'Crisis' Crossover
I had forgotten that she guests on Supergirl as Kara's kryptonian mom, so it's not that big a move for her to also pop up as Smallville Lois alongside Welling. That's great news though. The personal stories on Smallville were infinitely more fun once Lana went away and they could lean into Clark/Lois.
Also I know that Arrow's already wrapping up, but the big, huge, broad nature of this crossover makes me feel like they're doing a massive fangasm blowout on the potential that maybe Flash and Legends of Tomorrow wind down in the near future as well, making this a big farewell to the CW legacy of DC TV series.
Now all that's left is Rosenbaum returning as Lex. We don't need any more Lana, and there's basically no chance of a Chloe return given that Allison Mack has all that weird sex cult stuff going on.