Because I've been analyzing Fox gameplay for the past couple days, I'll post a cumulative list of what I have found by simply watching. I am Canadian and the closest demo was >2 hours away so I didn't get to attend.
Nerfs
-Fox's shine now lags more, quick on activation but you get "stuck" in it like in Melee, but the shine is not jump cancelable with or without projectile reflection.
-Uair knockback has been drastically reduced
-*Usmash knockback reduced
-Lasers appear to not cancel at all, unlike Melee/Brawl
-Fox's fall speed has increased
-Fox's Illusion now cancels when he moves over a ledge on the ground, meaning he can no longer traverse platforms such as the bottom two on battlefield without doing an aerial Illusion.
Buffs
-Illusion no longer puts Fox into a free fall, and he can use his specials out of it, but not use Illusion twice.
-Fox's fall speed has increased
-Forward Smash is faster, not sure on its kill power
--The last hit of Fox's Dair now hits upwards, if the move finishes before the final hit occurs, the move keeps it functionality from brawl
-Fox's laser appears to only decay to 2% at max distance from 1% in Brawl, but still does 3% closer up.
Unchanged from Brawl
-Fox's Foxcopter hover effect from Brawl is still possible.
-Fox's lasers have their same, terribad range from Brawl
-Fox retains his Utilt and Bair animations/moves from Brawl
-Fox retains his increased air speed
-Fox keeps his higher range Dsmash from Brawl
I know it's known Fox's Usmash was nerfed, but hear me out.
I was re watching some of the invitational and saw Fox's Usmash borderline kill Marth on the animal crossing stage at ~85% and the move killed Mario at ~100% on the Boxing Ring without an issue. Megaman proceeded to survive it on Wily Castle and the Boxing Ring really well, but PPMD had it staled on the Boxing Ring, and Wiley Castle has an enormous ceiling, and I also think that Megaman is quite a bit heavier than we think.
With regards to Fox's Dair, I am unsure whether or not it is only the last hit that send upwards, or the move will always send targets upwards when the move ends.
I watched the Nintendo Treehouse yesterday and the only match Fox was played in I saw him Dair Rosalina and land before the move had completed and there was no upward knockback. Thankfully, I would treat this as a buff as @
Splice
was explaining, but I was unsure of how it worked until now. If his Dair still autocancels on Battlefield etc. then this could be a buff to his juggle game, combined with his lower knockback Uair. This also means he can likely still Dair>Utilt, Dair>Jab and Dair>Usmash/Dsmash at higher percents.
I'm probably missing things, let me know.