Three possible scenarios.
- Diddy, Sheik, ZSS, and Sonic remain in the top 4 and combat each other. Everyone else below them combat for their placements as the meta develops.
- A character develops so strongly that they break the top tiers (most likely going to be Pikachu).
- The meta drastically evolves and our perceptions change. This'll only happen if new and usable tech gets discovered.
While option two can happen since Pikachu is really good in this game, I find he'll just enforce option one. I'm doubting anyone below them will be as lucky to have some sort of hidden tech that'll blast them to top tier. The best we can do is hope that history won't repeat itself and the gaps between tiers are minimal.
I can see Pikachu joining the top 4. At this point, I think we're going to end up with something like the following.
In Brawl
Broken: MK, ICs
Dominant: Falco, Diddy, Snake, Marth, Olimar
Good: ZSS, Fox, D3, Pikachu, Wario, Lucario
Not viable at the absolute highest level, but good: Wolf, Pit, TLink, Rob, probably missing a few (DK maybe?)
Everyone else is bad. The "good" characters are good, but only somewhat viable.
In Sm4sh we can already see differences
Broken:
dthrow uair
Dominant: Diddy, Sheik, Rosalina, ZSS, Sonic, Pikachu
Good: Ness, Yoshi, Fox, Luigi, Mario, C.Falcon, Robin, ROB, Greninja, Bowser, Lucario, TLink, Villager, Mega Man, D3, Ganon, Olimar, Pit, Dark Pit
Not viable at the absolute highest level, but good: Literally every other character
I've obviously missed a few in both scenarios, but at this current point in our metagame we already have FAR more good characters and more 'top' (dominant) characters which means there's fewer polarising matchups in the game. Some players put in work with their characters who are arguably not good enough for the highest level in Brawl, Seagull's an example that comes to mind because his Wolf was incredible. I see the vast majority of characters in Sm4sh being at Wolf-esque levels of viability and prolonged popularity. We will end up with characters that are undoubtedly on the bottom of the tier list, but the difference between them and a mid tier character will probably be far lesser than the difference between Ganon and Wolf in Brawl.
It's for this reason that I'm not concerned about a dominance from 4 or 5 exceptional characters, as the difference in quality between Diddy and Ness/Yoshi/Fox/Whomever in Sm4sh is almost certainly smaller than the huge gaping difference that occured between MK and Falco, or Diddy and Wario in Brawl.