I saw the Mario-themed Rabbids as an additional confirmation. I don't think they'd be allowed to make those without Nintendo's permission, judging by how harsh they are with usage of their IPs.
I was also very pleased with how often Rayman appeared. I didn't expect much. The top of the screen at 2:19 (and maybe the left side) looked new to me, so I'd like to see more.
I'm excited for this crossover, especially if it uses UbiArt. I don't like RPGs much, though. Rabbids Rumble was pretty fun, and I liked how it still had minigames. I expect this game to have more than just fights.