Wonder if this had been talked about before - but what of your personally wanted newcomers or characters have you come to feel like are just not in the cards realistically anymore, or had their chances gone since past games?
Currently to me, I've long come to feel the characters I've been wanting the most since Melee and Brawl just have had no chance in Smash anymore due becoming too codified on the NPC-roles they're given, or passed over due myriad of following factors.
1 - Dixie Kong = Lack of Interest on Moveset Potential, and Apathy on DK Series
Despite being explored as possibly being a duo character with Diddy before getting cut, Sakurai hasn't ever bothered revisiting Dixie ever since, making me personally believe he views her with having not much interesting to go off on her own (even with her ponytail, it's just isn't enough or even noteworthy for him.)
On that end, there's also me observing how Sakurai personally hadn't been interested on exploring DK-series series since Brawl to give it more characters, if going by how it took us the Smash Ballot to give us K.Rool - whilst glossing over potentials of Cranky Kong as a new unexpected retro rep that'd also allow the OG Donkey Kong of arcade-era be on the roster, and even Funky Kong as a possible echo/semiclone.
2 - Toad (Captain or Reg.) = No Inherent Moveset Potential => Codified NPC for Peach's Special Move since Melee, possibly for foreseaable future.
As someone wanting Toad since Melee-days, I feel like Sakurai has just never seen Toad beyond being an easily frightened little guy representing many interchangeable ones of his kind as we see him in first stage of Melee's Adventure Mode.
Even past Captain Toad getting his own game, the playable appearances of Toads in NSMB-games, his solo playable roles in SMB2, SM 3D World and probably most interesting of all, Wario's Woods - none of them has made Sakurai to consider him again for a fighter status, making it easy for him to move on working on Rosalina, Bowser Jr and eventually Piranha Plant over him. The very last one has definitely told me enough that Toad's just not inherently interesting character for him to explore, possibly since Melee-days. Maybe Toad's just that kinda everyguy NPC and thus, this is the best he'll get, especially with Captain Toad's train having gone by a decade ago now?
Ultimate making Toad be more active in Peach's moveset seems to make me wonder should I wish for Toad to grow more active in Peach's moveset enough to make them to a duo-character, but that itself feels pretty unlikely due being parasitic (no pun intended).
3 - Takamaru = Too Obscure To Be Playable. (Same for Starfy, Lip and Isaac)
Pretty self-explanatory as Sakurai had said so himself about Takamaru. But to me, it's bit saddening as it feels like this is what the characters like Takamaru, remain as, possibly for as long as the series keeps on going - unless he becomes the new "retro rep" in Smash 6 (which by that point, would maybe feel too trite for Sakurai to do after Piranha Plant letting him experiment in very new ways while sticking on a prime IP)
The only way for them to get possibly out this status would be to receive a big revival or reboot enough to make the series go out of the C-List tier to B-List, enough to stand in level of Fire Emblem or Xenoblade for example. To quote a certain ogre: "Like that's ever going to happen".
(Little Mac meanwhile had both luxury of a recently new game and a moveset potential that just happened to interest Sakurai at the time based on Mac's Assist Trophy-based moves in Brawl.)
I've kinda come to feel relatively accepting and ambivalent on too-obscure series or protagonists to have a playable spot in Smash in general, especially those very much more active in Japan-only territory p but I can't help bringing up above point especially, as it basically makes obscurities just mere "museum exhibits" in Smash in the long run, and make them lose much intrigue after people becoming mainly familiar of them on being Smash... and nothing else.
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I kinda do hope to see more character reworks of existing ones I already like to play as, but it's kinda clear to me how I'm not that excited for next Smash outside of it being a possible rebooted entry, which could mean a new, refreshed take on things we haven't seen a while or could use reworks, especially older characters dating way back to 64's Smash.