I can see them recon it so they could do another Crisis with Thawne in 2024, perhaps as a part of the final season, should they go that route.
Now as far as 2019 Crisis on Infinite Earths, I mean, do I have to choose one?
Supergirl 5x09 - A great introduction to the crossover with a good amount of references to the comic as well as the vast 50+ year DC history from current TV series, 66/89 Batman, 1978 Superman film, and the original 1985 Crisis comic. Green Arrow's early heroic sacrifice was a gut-punch to be sure.
Batwoman 1x09 - Smallville cameo, Earth-96 Routh/Reeves Superman, and of course Kevin Conroy's first live-action Bruce Wayne. Obviously great seeing all the Bats and Supes enjoyment given throughout, though I admit I do wish Kevin's Bruce was given a good Bruce to portray. But it was a nice twist. Absolutely loved hearing the old theme music!
The Flash 6x09 - Flash Vanishing, Black Lightning's Arrowverse debut, and Lucifer Morningstar. 'Nuff said. Don't have any complaints here.
Arrow 8x08 - I suspected Ezra was going to appear back in 2015, but his cameo still caught me off guard. Seeing Oliver as the Spectre was a plus, and Barry's learning of what happened in Elseworlds was satisfying and good continuity.
Legends Part 5 - Not my favorite episode, but seeing the new universe was pretty great. Liked seeing that there is a multiverse but no one knows as of yet...can't wait to see everyone's reaction. Also, not gonna lie as on old DC fan, GLEEK!
But for the sake of argument, if I have to pick one, the Batwoman episode, with Flash's episode having a slight edge.