I thought I'd go through my complete thoughts on Isaac's chances in Ultimate in one post. Here we go, let's start with the collected pros and cons listed from most important to least important. I won't be including any "leaks," as I believe those are fake until proven real.
Pros
+ He's first-party Nintendo. While 3rd Party characters are obviously possible, Smash has always given emphasis and priority on Nintendo's history. Easily the best thing he has going for him.
+ The Ballot. Sakurai has confirmed that he used the Ballot to decide the cast, or at least most of it. This is extremely good for Isaac, as the Ballot was his best shot since he did have a major push to vote for him. The exit polls show that Isaac is currently #1 overall from that data. While it's not conclusive, it's a very good sign of his performance. The demand is there.
+ The potential for a moveset is enormous. Seriously, there is no limit to what they can do with Isaac. He brings something very unique to Smash, and anyone who played even a bit of Golden Sun knows that his sword doesn't define him, it's his Psynergy.
+ He's been in Smash before. He was an assist trophy in Brawl but removed in 4. However, this can only be a good thing for him. The assist trophy shows that Sakurai and Nintendo are aware of Golden Sun and Isaac. His removal in 4 only caused people to want him more, and made it so it would be harder to just bring him back as an assist in Ultimate.
+ His franchise was very well received, and pretty popular at it's time. The Golden Sun games were some of the best games the GBA had to offer, and Isaac is the main face of that. While Dark Dawn wasn't amazing, it wasn't horrible either. There's even the fact that there are pictures of Golden Sun on the boxes of GBAs. It could bring more GBA representation to Smash, because it needs it.
+ The hints. By no means is any of the hints we have conclusive in any way, but they are pretty convincing when put under a magnifying glass. The tweet is the most obvious, and honestly if there's one thing it's referencing it's definitely Golden Sun. Sakurai has told us before that he never just tweets randomly, and this seems very random if it's not a reference. Sakurai has also shown us that he can totally drop subtle hints like this, with the "red eyes" and the barrels in the background. There's also the big, dare I say "Golden" sun at the end of K Rool's trailer. It's flimsy at best, but worth mentioning. If nothing else, all that got people talking about Isaac.
Cons
- He wasn't super popular in Japan. He was still popular, just not as much as in North America and Europe. Not sure how this will affect him.
- He does have some competition. Only so many characters can make it into Ultimate.
I noticed while writing this that I just couldn't come up with many good cons. Why is that? Well, almost every con associated with Isaac has been completely disproven by Ultimate. Stuff like him being "irrelevant" don't matter anymore, and that is why it's looking so good for Isaac right now. Nothing is a sure thing and I think we should keep that in mind, but the chances have never been better and I feel like now is finally the time.