EDIT: Primal beat me to the Sunday/Charmed promo.
Glad to hear the Legends are sitting this crossover out. As I said on that board, the last act of these crossovers always feel bloated to me, largely because the rest of the Legends cast that had been sitting out the previous episodes suddenly show up for their glorified cameos.
I'd prefer fewer supporting cast members in these crossovers in general, tbh. Give me one with just Kara, Ollie and Barry on Warworld or something. One where they actually have to interact and get to know each other on some level. I think that's why I liked the musical crossover more than the others: it gave Kara and Barry quality time together for actual bonding and character development (even if I didn't care for that particular character development, lol).
Also for the record, I don't think this move to Sundays will be good for the show, ratings-wise. CW tried Sundays before, and it tanked. The only way they might have a shot at not tanking is if they put their flagship show (Flash) there, imo. They already hurt SG's ratings with the hiatus, it's not in the position of strength on the CW's line-up that it once was.