This could be my personal bias, but I don't think Min Min is near the top of the list to return.
While no first party series have been cut in Smash history aside from Icies in 4 due to 3DS tech problems, I feel like that's less a solid rule and moreso something that just hasn't had a chance to happen yet. Since Ultimate by its nature didn't cut anyone, the most recent step in this line of thinking was when no first party series were cut from Brawl to Smash 4. There were 33 First Party Vets then, now there are around 66-71 depending on how you count the miis and swap characters, literally double. In comparison to the number of series represented, there were 17 first parties series in Brawl with a fighter, compared to 25 now in Ultimate.
Put simply, 'all first party series should be brought back' just because it happened from Brawl to Smash 4 and ig Melee to Brawl just doesn't seem right to me given how different the playing field is. I haven't mentioned third parties yet, but they've come to cut out a larger and larger piece of Smashes roster as it's gone on, so the question of how necessary any one series is in terms of cuts has to be different now than it was then considering Brawl had just 2 Third Parties to consider, whereas Ultimate has 15 on the table with three having a secondary rep.
Min Min then, being so incredibly unpopular to fight, especially in Japan, I think genuinely might be solid reasoning for Sakurai to look over her when bringing other fighters back. I see Sonic not being cut mentioned as reasoning as to why this wouldn't happen, which I can see the logic in, but he's Sonic, I think it's fair to say he has bit more going for him outside of Moveset then Min Min does.
I guess to sum up, she just sorta fell on her face from the hype on reveal, to the moveset she got, to even the kinda unfortunate fate of ARMS as a game and series. I'm not a prophet, and the game still sold well enough to warrant a Smash inclusion a few years later, so idk, but I just don't see Min Min as a safe choice to stick around, especially if one of the best things going for her is simply that we haven't seen someone in her category come and go. If anything, I think that may be evidence she should be one of the first out the door, but that's just me.