I think it's safe to say that, of all the potential Smash newcomers, Toad has had it worse than most others if not the worst. For three games straight he's been relegated to a rather undignified (and frankly useless) position as a counter, despite his relevance only growing since the Melee days with more prominent appearances in both mainline and spinoff titles. Only in Ultimate is he given a slightly more respectable position, but even then, the bar was set pretty low for him and I'm not prepared to say that his current situation is a massive upgrade.
The arrival of Captain Toad further complicated the situation. I'm not sure how others felt at the time, but when I first encountered him in Galaxy, I thought he would only be a one-off character (I honestly wasn't expecting him and the Brigade to even reappear in Galaxy 2). Naturally, I was delighted to see both him and Toad appear as playable in 3D World, Captain Toad in particular receiving a notable upgrade from side character to the face of his own minigame. One could probably imagine the wonder – and shock – that came when he (and the honorable Toadette, of course!) received their own game. It felt like a dream come true! Though it's been an uphill battle for Toad/Captain Toad and his fans, his future is looking fairly bright: a respectable role in Odyssey, ports to two of Nintendo's most popular consoles, and even promotional material/his own artwork in the company handbook seem to indicate that the Captain is here to stay.
I might be making a bold assumption here, but I think a lot of us want Toad/Captain Toad in a Smash so badly – besides his moveset potential, obviously – because we've found the Toad character to be particularly endearing. Whether Toad's your Mario Kart main, Blue or Yellow Toad is your character of choice in the New Super Mario Bros. games, or you're knee-deep in Captain Toad: Treasure Tracker, it's safe to say that a lot of us have some sort of an attachment to him. I say all this for one reason: look how far he's come! Smash or not, Toad's become even more important to Mario – and by extension, gaming – than he ever has been before. Yes, it would be wonderful to take Toad or the Captain to the battlefield, but no matter what happens, we'll always have plenty of games to remind us what makes Toad super. Sucks to say, but a lot of Smash fighters, new and old, don't have that going for them.
Plus, after Ultimate, we have to rally for that Treasure Tracker sequel.
(sorry this is kinda shoddily written I don't do optimistic posts very often)