Looking back on Ultimate, one thing that felt kind of underused was the Present menu. I mean, I get it - much like with amiibo, they're kind of stuck between a rock and a hard place when it comes to doing anything with it. Do too little with it (like amiibo post-Wii U), and it feels pointless, and do too much with it (like how some people viewed amiibo-exclusive content like the Fusion difficulty in Metroid: Samus Returns) and people complain because it's locked behind a paywall.
I just feel like more could be done with a menu like that than just giving us six spirits and a single music track. I get it - they probably don't want to require people to buy whole games to get all of the content. (though it's nothing new for the series - Melee required you to have Pikmin 1 save data for 100% completion)
I just figure something could be done with smaller downloadable titles. People might be annoyed by a song being locked behind a $60+ game, but it doesn't seem like it would be as big of a deal if, for example, buying the Switch versions of Dragon Quest 1, 2, or 3 (any one of them, so you have three options and they're all cheap) unlocked the
Dragon Quest Overture, or buying any version of Shovel Knight on the Switch (Treasure Trove or any of the individual releases) unlocked
Strike the Earth! Plains of Passage, or buying either of the Bayonetta games unlocked
You May Call Me Father or
The Greatest Jubilee, or buying any of the countless Sonic games on the Switch unlocked
Chemical Plant Zone if they couldn't include those songs in the base game (or in the initial DLC release) for whatever reason.
I'm not familiar with the music of Final Fantasy 8, 9, or 10, but I'm sure there's some stand-out song that could be included so that we can get some content from Final Fantasy games beyond 7. (also, how haven't they released FF1-6 for the Switch yet? That seems like a no-brainer)
I'm not sure how possible it is to do something like that, but I figure it would be nice to give the player more than one option to get that content. (plus, due to the timing of Joker's Smash release compared to the release of Persona 5 Royal, we couldn't get
Take Over in Smash, which is a huge missed opportunity; getting Sophie's spirit early was nice, but unlocking Take Over in Smash on top of that would be amazing)
Admittedly, all of this is a minor quibble at best, and the game is amazing, a testament to how far this series has come since the N64 days.