She already is in the mascot league with the rest of them.
Like
why
do
people
still
struggle
to
accept
that?
Seriously, she was insanely popular when she debuted, and her popularity has only gotten bigger since. She actually started off more naturally popular than most other characters.
She's also hitting her 10th anniversary next year.
Rosalina is here to stay and at this point, it's becoming close to a point where Peach and Rosalina are interchangable as the main female mascot of Mario. Notice how for the platformers and stuff, they use Peach more since you save her and because it's tradition? But then when it's been a spin-off lately, it's Rosalina who takes prominence?
This is because Peach isn't exactly a good female face for a franchise in this day and age, and Nintendo realise this (her absence on the Women's History Month promotion hits that home in particular). However, she's been with the franchise for 30 years, so they can't exactly just up and give her the boot, because that would confuse people from a branding standpoint.
That's why, for the platformers and RPGs, Peach is more prominent, since she's so ingrained into the legacy of those games. However, in everything else lately, Rosalina has easily been more prominent, from Mario Kart, to Smash, to Tennis, to the Badge Arcade. That's because Peach has never been as prominent in those games and is just sort of a by the numbers inclusion. It also means they can use Rosalina as a more empowering female, which is good for their marketing, as that's what people actually prefer in a female character these days. So they keep to tradition for the main series and RPGs since people expect that from them, and expect Peach to be there. But in anything else, they switch out for Rosalina as the more prominent figure, since she is a more positive role model, and they know she's the fan favourite.
Wario and Toad really are not comparable to her either. Wario got his own two franchises but they have been fizzled out. Now he's just spin-off fodder, just slightly better off than Waluigi and Daisy because he gets into Smash. Toad is a stock race rather than a specific character. Easy to implement onto merchandise because of his simplistic design, but Toads are just "there" in most Mario titles, unless it's Captain Toad.
He is not fond in any way of Rosalina tbh , and her inclusion in recent games are purely fan requested. Rosalina is not really a big character , but she is amoung the the most popular ones within the fanbases and Nintendo as a company knows this , so this helps her get her way in promo materials.
Miyamoto is over his dislike for Rosalina, and the team at EAD loves her to death, according to two certain interviews.
She is definitely a big character and EAD fully intend to keep using her.