I think Simon made it in because he's ultimately the most iconic character. Alucard may be a bit more popular, but Simon has more prestige and historic significance to him. Pac-man isn't in there because he's everyone's favorite character, he's there because EVERYONE knows him, and it really doesn't get much more historically significant that him, at least not for playable characters. Or how about Duck Hunt? Again, definitely not everyone's favorite character, but people know the game, and that dog is iconic. Alucard is in my opinion a bit cooler, and looks, again my opinion, like he'd be more fun to play in Smash, but he just isn't in the same tier of iconic historicness as Simon.

Trust me, I get why you'd want him. I've played enough Kirby games. He makes more sense for the next Kirby rep than any other character from the series really. But again, pretty much every reason you give for BD is a reason for Toad, and yet Toad is still stuck in Peach's dress. I'd argue Toad is a bigger deal of a character. That said I could see him getting in over Toad just based on that Japanese poll. If that is in fact reflective of the Smash ballot for Japan, that boosts his chances. But I'd want to see the other regions choices, because something tells me BD would be a polarizing choice, popular with some, but seen as an utter waste by others in a way none of today's direct's characters were. I also think Sakurai is trying to please more than just Japanese fans, and may even be leaning more towards Western interests with this iteration of Smash. I wouldn't rule him out, but I'd put his chances at well below 50%.

We still got isaac, saki, isabelle not confirmed yet too! And Dillon

I must admit King K Rool was a suprise for me but i expected Simon Belmont. I have a feeling a Resident Evil character might make it in and most likely Leon Kennedy. He made it big on a Nintendo system so i cannot see why not.
I also have a good feeling a Rare character will make it across aswell due to Nintendo and MS's recent relationship.

Hmm...
Obviously I would really love Shantae, but honestly, I'd be ecstatic if she just got a trophy or something.
Also Tails as a character. Hands down. Especially if we get Shadow as an echo fighter.

I don't expect anything at this point. I'm completely content having the roster as is and basically all my character bases have been covered.

I mean, at this point, with better representation for Metroid, the new looks for Link, Zelda and Ganondorf, existing characters like Lucina and Dark Pit becoming echoes, Chrom being an echo, the two Belmonts being added, K. Rool finally joining Smash, Inkling being added, plus the ridiculous stage selection, excellent array of assist trophies, the promise of a 28-hour soundtrack, the sheer range of options, and the return of Classic mode, asking for more fighters almost feels greedy... but there are more I'd like to join. Personally my biggest hope at this point would be that the 'Spirits' mode really is some kind of single-player campaign.

So, in terms of other characters I'd like to see, I'll suggest first party then third party characters. I'm happy with the roster as is, and honestly don't know how many more to expect, but I'd be open to all of these characters coming as DLC.

I'd like to see Captain Toad and Rabbid Peach join; Skull Kid or Midna & Wolf Link to make the transition from assist to fighter; Arms get some representation (Spring Man or Twintelle); Rex & Pyra/Mythra join as a fighter; and Dixie Kong as a Diddy echo.

From third parties, I'd like to see any out of or several of: Monster Hunter, Amaterasu, Leon Kennedy, Doom Marine, Dovakhiin, Crash Bandicoot, Rayman, Dr Robotnik as fighers; Shadow as an echo for Sonic; Ken or Akuma as an echo for Ryu.

Finally, there's one stage I'd like to see: Mira, from Xenoblade X. A platform could start you in the New LA hub, and then fly you randomly from continent to continent across Mira.

Doom Guy/Slayer should make an appearance. Even as a assist trophy. Doom has been big on Nintendo since the SNES and still have Doom64 which was exclusive. Now with Switch obtaining both Doom 2018 and its sequel, there's really no excuse not to have him. His one of the all time classics.

Oh shoot, I forgot to add:

Megaman X as an Echo Fighter
Solaire of Astora (He's getting an amiibo)

Yeah. DOOM Guy is one of those characters that, just like until only recently Simon Belmont, is honestly pretty crazy how they haven't gotten anything in Smash yet given their long history on Nintendo platforms. Really hope DOOM Guy can make it into Smash Ultimate, if not the base roster then at least as DLC later on. 

Seeing as how recently Nintendo and Bethesda seem to have a really good relationship with Bethesda supporting the Switch so much, maybe the chances are better than ever, and like you said with DOOM and eventually DOOM Eternal being on it as well. 

The “Add Goku!” trolling is getting older than All Your Base are belong to us.