I think that somebody should try to analyze data and try to speculate what the tier list may be... I think that may be a fun project for people to do
There are a lot of reasons this is really hard to do.
The most obvious is that we don't have enough data to even begin to judge most of the characters. The 36 characters not in the demo we have about 20 seconds of footage each on, and of course there are probably a few unannounced newcomers about which we know literally nothing. Every smash game continually reminds us of how one character can have a huge impact on the meta, and it's pretty likely characters like that lurk in the group of characters we just don't know much about.
The demo is of course not final, and some things that seem not final in terms of even basic mechanics would shape the list. Like the thing where you can't run through shields sucks really badly for Sonic. We think it's a bug, but if somehow it's in the final release, that will take him down a peg as it completely removes his ability to run through a shield and pivot grab which is a major tool for Sonic especially in a world where it's less safe to repeatedly spin.
Honestly a lot of characters in the demo weren't really done justice either. Ice Climbers are probably the best example. Almost every ICs player in the demo just loses, but then again, how could they win? They aren't using desyncs properly at all even though it's extremely visibly obvious ICs have those full capabilities in Ultimate, and they don't really seem to have even worked out the new properties of most of the ICs moveset which is double important on that character because it's the kind of character wherein sloppy play separates Nana and thus sets you up for a horrible situation. Of course, they couldn't really avoid that; you need time in the lab to avoid that, but the result is a lot of people saying they think ICs look like a really bad character when if you really think about what you're seeing and why all of the ICs players in the demo lose that's not clear at all so much as it's clear "you can't possibly figure out ICs in a demo setting". Even beyond weird characters, there's just the raw differences. For every 20 Pokemon Trainer matches, you can find 1 Pac-Man match if you're lucky. How good is Pac-Man in the demo? Well, he's buffed, and no one is quite sure exactly how much or how much it matters because almost no one even played him...
It's not to say we don't have some character quality speculation we can do. Based on what I saw in the demo, I have high confidence in Pikachu, Pokemon Trainer, Marth, and Ike. They could still be nerfed before release of course, but those four characters were just so good in the demo in a lot of basic, obvious ways that it's hard to see that not holding up into release if they're just left alone. Basically all of the characters who were top characters in 4 still seemed good, mostly toned down but not nearly enough to really change the story from a naive viewpoint. That was mostly good news for Mario, Sonic, Bayonetta, Cloud, and Sheik. I also was specifically impressed with DK and Snake; DK got large buffs and Snake seemed to transition well from Brawl which is a big thing since Snake was a top character in Brawl. Hopefully you see the problem already. This is a list of 11 characters who look promising in a demo of 30, and it's not to say that the other 19 characters look bad because a lot of them are promising in their own ways (like there's a real buzz for Little Mac in a lot of circles) or are the characters like Pac-Man or Pit that just weren't getting picked as much. Clearly things are going to break down more than this and some characters that appear good now, even if they don't get nerfed before release, are not going to work out because too much looks good now to possibly hold up in a more mature metagame.
I do think talking about the various qualities of the characters in the demo is a fun and relatively useful exercise (not like actually useful but relative to blind guessing who the newcomers will be), but we just have to be aware that our knowledge level here is really low and most of what we can figure out won't really be true when the game comes out so it's more about just having a starting point on day 1 than anything. The main starting point I figured out for me as a player is "I need to play Pokemon Trainer as soon as possible to figure him out for myself", not super great from a data perspective but better than nothing.