For me, the biggest reason I am ambivalent about Smash pursuing more crossover interactions is just the fact they take a lot of time. You have to ensure that all parties involved are fine with the way the characters are interacting, you have to make sure the characters feel true to themselves. It takes a lot of love to do it right.
It's similar to why I am fine that trophies are gone. I understand that it would be cool, but it is a massive drain on resources. You need to research the characters to make sure its flavorful and in character, localize these interactions for different markets, translate them, in some cases get approval of all rights holders, hire additional voice acting, and/or animate new cutscenes for them to work. I understand it would be cool, but its not something that I think is essential to Smash.
Similarly to trophies, the bulk of these crossover interactions (outside of ones with gameplay included like Palutena's Guidance or Codecs) will be happening most likely in Solo content. I feel that Smash at the end of the day is going to primarily be experienced as a multiplayer game. Yes, you do have classic mode and other modes, but the bulk of the average consumer's time with Smash is going to be spent playing local or online multiplayer. That doesn't mean Smash should have no single player content, that would be awful, but I feel like things like Trophies or in this case, crossover interactions, are best integrated in a way that plays to Smash's strengths.
Would I love extra character interactions? Of course. Part of the magic of Smash is it's natural absurdity. You have Super Mario fighting against realistic Solid Snake, anime swordfighters like Cloud, and Jigglypuff. A big part of why I think Smash pops for casuals, even if they do not have the same connection to the characters in the roster, is the visual diversity. Look at Bowser and Ganondorf side by side. Both iconic Nintendo villains, but so different in design and flavor. It's great to have vibrant, expressive movesets that help sell how these characters are from different universes. Seeing Link fight with his best gear from Breath of the Wild against bounty hunters from space or a guy with a butterfly net is just naturally silly. The trailers, Palu Guidance, and codecs all lean into this inherit weirdness.
...but do I need the development team to scratch that itch further? I would like it, but I can live without it. It would be cool to get ringside advice from Doc Louis when playing as Little Mac on the boxing ring or Futaba to give analysis on the other fighters while in Mementos. I would love a story mode that focuses more on using the characters in a crossover sense. But I do not need them. That is far lower on the totem poll of needs for me. I would rather see new areas come to life as stages. I would rather see new and old characters interact with that inherit weirdness of Smash existing.
I think wanting this stuff is valid, I would be happy with it too. But I just feel kind of lukewarm on it as of now. Maybe if they did go for that big dynamic story mode and made it truly work, I would be sold more. As things are, I just do not need them to go further.
