I'd argue it would be more than a cameo, but I get what you are saying. The comparisons aren't exact, but my main point is that Disney can be difficult to deal with, even with bigger companies. And that the potential complications might encourage Nintendo to go "It would be nice to get Sora in, but we still have a lot of fan favorites that would sell extremely well and would break the internet that we can negotiate for that aren't owned by Disney". I just don't trust Disney to not get greedy with this if it ever came on the table. And that in itself would create complications
I mean even though it does work that way there would still be negotiations on how much Sora would cost and if Disney would let Square get a portion of the cut because they work on the games Sora is from. There's still possibilities of complications
Sony's handling of Spider-Man with their own universe was annoying and I also have hated a lot of their decisions they've made. But with this deal specifically, I do side with Sony. I don't think Sony was completely dead set on moving Spider-Man to their universe yet because they wanted to renew the current deal they had. That was the deal they wanted to keep before the 50/50 deal was brought up. I'd also argue even if Disney was offering a 70/30 split, you'd still be losing money. Not as much sure, but it still wouldn't be entirely fair. Especially since I haven't found anything that stated that Disney would let them get a cut of the Spider-Man merchandise, as well as a cut of the crossover films Spider-Man is in
I get a corporations job is to make money. That's totally fine. Part of the reason I'm with Sony on this is because the 50/50 deal would've really not be financially smart to take. But at the same time, there does come a point where you end up pushing it and becoming unreasonable and even though I get you want to make money to invest in projects and pay employees, you can do so in ways that are reasonable which I don't feel the 50/50 deal was. Sony did benefit from the previous deal sure, but I don't think Disney was getting the short end of the stick because they still make millions with Spidey regardless. While the loss for Spider-Man in the MCU does hurt both companies, I don't think it's that big. Sony proved with Venom and ITSV that they're more than capable of making it without Disney. And Disney is well Disney. It's a shame about Spidey, but they'll both be fine
I just want to insert my two cents in here real quick on that Spider-Man stuff.
The latest Spider-Man movie crossed a billion dollars, and that's nice and all, but Sony does not get to take in all the money made from that film. First dollar is shared with Disney/Marvel, and that company now wants to see bigger cuts of the pie. Take that into account and consider the success of last year's Venom film, which grossed almost 850 mil (almost as much as Homecoming), with Sony getting a good chunk of that cash (Venom's success in China will likely please their partner, Tencent, who were involved with financing, marketing, and distributing the film over there) and Sony would have to consider which IP looks more lucrative and makes more business sense right now. Also consider that a proper Spider-Man vs Venom is also hot in demand, and an eventual fight against Carnage has event potential at the cinemas, one very key player is missing from this equation, and that's Spider-Man himself. I see a lot of reasons to take Spider-Man back beyond negotiation mishaps with Disney.
MCU fans will be mad for now, but going forward, I think the ball is in Sony's court and they can change public opinion if they play their cards right (and I have a huge interest in them doing so as I don't like the MCU or their version of Spider-Man). Spider-Man has a very rich universe. They have to get the right people involved and produce quality content. Unfortunately, we don't know what their plans are exactly at this time. They supposedly have 5-6 TV shows in development that are within the 'Spider-Verse' or SUMC (Miller and Lord are likely producing all those) and a number of movie projects rumored and confirmed to be in development (Arad, Tolmach, and Pascal likely producing those). We'll see what happens there.
For Sora, the situation is a bit different. Sakurai once said that they almost couldn't get the rights for all the characters back, and it's rumored Cloud almost didn't make the cut for Ultimate. To get Sora in Smash, Nintendo will still need to negotiate with Disney, as he's their character, even if they'd defer most of the decisions and supervision to Nomura (who designed Cloud and is heading the FFVII remake). If Cloud was a problem, I could see Sora being another big hoop to jump through since another big company will have to be involved, but Smash is huge, so it's possible. It'll probably come with limitations (like no other Disney characters/worlds), and how big those limitations are will account for whether Sakurai feels he can make a great fighter with him or not, and whether a stage should accompany the character and what music can be included. And of course money will be important. If Sora is too expensive to get, when other IP's are cheaper to license (or just include Nintendo's own highly demanded characters) that can play a role on whether they decide to jump through that hurdle or not.
As for audience, going around youtube, I do feel female gamers/streamers are particularly interested in having Sora join the roster. They're not a particularly huge base for Smash, but I think Sora will bring appeal to that crowd with his inclusion. Whether his inclusion would be best for DLC or a whole new game is another question, but since Sakurai wants to expand on a cross-over record here, they might at least gun for DLC if Sakurai thinks Sora would fit well in Smash.
The future is anyone's guess right now. Negotiations are going on as we speak, and development on these additional fighters beyond pack 5 has no doubt already been underway. Who did they choose? We might get a peak or hint at the end of this year, or we'll probably have to wait till the next to find out. And then speculation and requests will continue from there. :D