Although it's a crossover, Nintendo nor Sakurai seems very interested in the aspect of crossover interaction outside of a story mode, just that the crossover exists. You've seen a million tweets going "
Imagine showing someone this 10 years ago" with all the third parties, they usually don't care about the interactions, just the thought of them coexisting in the same game as it is. There are easter eggs with guidances and codecs, but that rarely shows much.
I don't expect a crossover interaction in the base game without using hidden taunts or win quotes, just only in story mode events. That's just for now and in the future. It's a shame too, Subspace was perfect with character interaction without voice lines, and Ultimate seems to have gone for the upgrade of
adding voice lines.
Lots of hypotheticals though, I would've liked to see Lucario and Ryu interact. Mostly just because it's dub Goku and Gohan.