After being around the game pretty heavily for about a month now, I'll post an educated guess on what I think the tier list might eventually look like, also as something to look back at later to see how accurate/inaccurate it was:
S:
A:
B:
C:
Diddy and Sheik deserve their own tier because they both have massive strengths with no real weaknesses. Sheik's KO power isn't that bad considering how deep offstage she can go and how safe up b seems to be in many situations.
Yoshi similarly has no exploitable weaknesses but his strengths aren't as overpowering as the former two, while Sonic has a terrible aerial acceleration and, while annoying, fairly punishable approach options. Rosalina on the other hand is pretty much helpless without Luma when its capitalized. ZSS, Ness, Pikachu and Fox all have solid setups and projectiles that won't go away no matter how much the metagame develops, making them solid picks for characters as well, with some quirks to balance them out such as Ness' bad recovery or exceptionally light weight for the other three. This is where I'd draw the line if A tier was divided into A+ and A-, because this is where characters start to have more apparent weaknesses.
Villager is definitely A tier, and the only reason he's not considered better more widely is because of a lack of representation at tournaments (Salem or somebody
pls change this). He has limited close combat options but in my opinion the most dynamic projectiles in the game and a strong offstage game with his great aerials and recovery. Lucario mains seem to be focusing on his nerfs while everyone else is focusing on what aura can do at its best. Disregarding both, I think he's comparable to how he was in Brawl compared to the rest of the cast. The focus moved slightly more into keeping him alive at high %s, and he lost some reach while gaining speed on his moves. Falcon has a bit of under-representation as well despite good players occasionally picking him, but once someone really focuses on him and puts his mobility and 50:50 traps as well as true combo Knee setups to good use people will see just why he really is so solid. He has an exploitable recovery, but he also has something where other high speed characters are lacking which is strong kill power.
I'm just assuming Dark Pit and Pit will eventually have similar effective capabilities despite their attributes being tuned somewhat differently. Mario is an all-around good character with solid throw setups, while Luigi has awkward movement and aerial speed, but is a killing machine once he gets in with his throw setups, smashes and even up b. I feel like he's a Mario with more extreme pros and cons and no cape. Mega Man is probably the second best zoner in the game with better close-combat options than Villager thanks to his fair, bair and especially a solid grab. Wario is someone I haven't seen as much as I'd like, but he doesn't seem to have any considerable weaknesses and his overall aerial mobility is arguably the best in the game, as is his height/weight ratio. Rage also helps him more than anyone else in this tier, Falcon being 2nd in that and Ness/Mario/Luigi 3rd.
B tier I'm the most uncertain of compared to the other tiers. I basically drew the line where the seriously good grab games and setups end or where more considerable weaknesses begin. Aside from Diddy and Sheik, I think these characters can still easily compete with A tier, but just aren't quite as solid overall. I'm the most uncertain of Greninja, Peach, Pac-Man and Bowser Jr. in this category, but I have the perception that the first three are at least good, DHD is decent and Bowser Jr. isn't terrible. Meta Knight, Olimar, TL, Marth and Falco got nerfed quite hard and partially because of that are being slightly slept on. They aren't
that bad. Rage helps Bowser, Dedede, DK and Ike a ton, but big frames and/or slow speed are very fundamental weaknesses, although Bowser moves really fast (and as a side note has great OoS option in up b), hence having the highest viability out of those. I feel like they gave Robin slightly too much weaknesses to balance out his/her strengths. A slow running speed, limited close-combat options and a short (although quick) grab aren't a good combination. I'm kinda still
feeling out Shulk, but the control the player is given with him shows potential. He has slow attacks but a lot of range and some good autocancels to complement it.
C tier is where huge weaknesses or overall mediocrity begins, but they can still have plenty of good match-ups vs all of the higher tiers. Mac still seems decent for now, but this is one case I feel will change once people start to truly capitalize on his non-existent recovery and aerial options. He still has pretty much the best ground game of course, but that won't help him half the time. Ganondorf strikes the hardest hits in the game, but it doesn't matter in the match-ups where he simply can't get in. These two are above the rest because they have these niches, and the rest are basically the "mediocre" part.