Ok so people who are smarter than me, how does this affect Doomguy? Asking for a friend.
About the same as ever..which, in my opinion, isn't very high. Doomguy wouldn't really appeal to the Japanese audience at all (even Ridley, K. Rool, and Banjo appealed to a lot of Japanese, even if they were mostly put in for the West), as well as Shooters not being that popular in Japan either. I feel Doom's role in gaming history is significant enough to deserve representation (I use that term loosely since no one 'deserves' to be in Smash, they just are or aren't), but there's other much more popular 3rd Party characters that are not only popular, but popular worldwide, such as Sora from Kingdom Hearts, Crash Bandicoot, and Heihachi Mishima from Tekken.
I don't really see anyone talk about Steve like that, since his chances seem to yeeted into nothingness since Banjo's in this time.
We'll have to see if Spirits deconfirm or not. They probably do, at the very least for DLC, unless we get a Season 2 along the lines of SFV, T7, KI3 and DBFZ. Obviously, some of the characters I shill are spirits so I'm hoping a PNG isn't a big deal if Lucas and Mewtwo having trophies last game before they became DLC later on. On the chance Spirits don't take someone out of the running, then Dixie or BWD would be good choices because they've been popular for a minute.
As for the Pokemon, I don't know if being too late is that much of an issue, but it might be. I don't know what Pokemon would be chosen because there's not much in the way of standout Pokemon for Gen 8. I'm sure they'll be a really cool Pokemon people want to see, but I just have no idea who it'd be yet.
There's also the chance some retro character gets brought back, but there's not much discussion going with that. It's clear you've got an issue with the lack of first party discussion going on, but when every returning character is back, and we get quite a few really big fan picks like Ridley/K.Rool/Chrom, AND some of the other ones like Lyn or Isaac are still Assists, it's hard to get people engaged in stuff they aren't interested in.
In my opinion, knowing what we know of Ultimate's DLC Fighter Packs, while I think that Spirits do deconfirm, its not for that singular character having a Spirit, but their series in general having a lot of Spirits. Let me explain.
We know that all DLC Fighters will, evidently, be coming with 4 things: the character themselves, a new stage, new music, and new Spirit Battles.
While the middle two aren't helping any series already represented (for example, we already have a lot of Kirby stages and musical selections, there's not much reason to add more), but the Spirits is the bigger issue.
Lets use Rex & Pyra as an example, even if they've already been soft deconfirmed by Sakurai. What could they have for their Fighter Pack?
The Character: Naturally they'd be this..so good here.
Stage: No Xenoblade Chronicles 2 Stage exists, still good.
Fighter Spirit: While Rex & Pyra both have solo spirits, their fighter spirit would be them together, which would be different..so still good.
DLC Music: While some XBC2 songs are in the game, there are more in the OST to use, so still good.
Spirits: Almost all of the big, important characters in the game already have spirits..this would leave only lesser characters for Spirit Battles..in my opinion, this hurts their chances significantly.
So if you look at every series already represented in Smash Bros, almost all of them already have a lot of Spirit Battles for their series, leaving little to no Spirits to use for the DLC Spirit Battles, outside of maybe Fire Emblem: Three Houses or Pokémon Sword/Shield (and Final Fantasy VII..lol) since those games, of course, have entirely new casts/Pokémon to pull from for Spirit Battles..though I don't personally believe either series will get a new DLC rep.