Let's start with me saying that I love the new Final Smashes, quicker, strong and straight to the point (and I am a sucker for cinematics).
The only complaints I have is that Jigglypuff still has the same Final Smash which doesn't fit her (as it isn't even a move) and easily avoidable. Ice Climbers and Bowser Jr. could've been upgraded a bit as well (Iceberg could've been upgraded better).
Donkey Kong's new Final Smash is cool and all, referencing how you defeat a boss in the new games. However it is very similar to that of Little Mac, and I rather would've seen a cinematic in which he pulls the opponents into 25m and throws a barrel at high speed at them. But nothing that can be changed here.
Now the character that have a transformation Final Smash and I think are 100% certain to change:
- Yoshi - Mega Eggdozer seems like a good one for him
- Diddy Kong - maybe grab the guitar and play a quick tune, a quick strong version of Konga Beat, referencing DK64
- Lucario - I think he will Mega Evolve and perform his Final Smash from Brawl (mixing the two)
I think these characters will probably stay the same:
- Captain Falcon
- Meta Knight
- Wii Fit Trainer (as they said she didn't change that much)
- Duck Hunt
And lastly the ones I think/hope will change:
- Peach - something with the vibe scepter from SPP, otherwise perhaps a beam of love or something cheap like that
- Young Link - doesn't have one, so hopefully a transformation into Fierce Deity Link and deliver a few slashes (then at least all Links have a different FS)
- Greninja - most likely to stay the same, but why not take the oppertunity and turn it into the Hydro Vortex Z-Move?