If they include Digivolutions, it would probably be for a Final Smash.
I doubt it'd only be for that. It's literally the core concept of what made Digimon stand out overall. Training in general is a general mon thing, but having the ability to go into multiple forms throughout battles is what really made the series so iconic. And not just one straight form like Pokemon originally went with(and Pokemon only slightly did split evolutions. Nor could you de-evolve, a concept unique to Digimon at the time).
Digivolution is basically an iconic part of the series. So is raising, but that's a very common concept that's harder to make work in Smash. Not that leveling up in battle is impossible(Lucario has something similar), but it's difficult to implement in a balanced manner.
The Final Smash only makes sense if we're talking about a Warp Evolution like WarGreymon, or a Warp DNA Evolution into Omnimon. Both are his most iconic Mega forms, and both work depending the direction they want to go in. It also helps that since he can de-digivolve easily, you can apply a somewhat Pokemon Trainer-esque moveset for switching out, or possibly he de-digivolves under certain conditions beyond being KO'd(which could put him into base form or the previous form, if we're using Greymon and MetalGreymon). Digimon also has introduced the ability to use cards to use other attacks, but that's something that would make more sense with a Tamer's related character, like Renamon or Guilmon.
Worth noting that the anime is significantly more popular than the games, which is also why Digivolution is seen as the most iconic thing.
(To note otherwise, Evolution and Digivolution are the literal same thing if you're aware of the Japanese names. Digivolution is a dub-only thing, but it is kept consistently throughout every anime, even the later movies who get rid of the "Digimon Digital Monsters! Digimon are the Champions!" theme song. Though to be fair, licensing is not easy anyway).