Sounds so farfetched. Nintendo would be more likely to just hoard the IP than sell it. And if Platinum had the money to buy the rights from Nintendo, then they should have had the money to port the game without a kickstarter too. They'd first have to buy the rights before they can start a kickstarter and that comes with the risk that the kickstarter doesn't bring in enough money to finance the port(s), so the money spent on the rights would be wasted. But it's Kamiya's brainchild, so maybe the financial risk didn't matter too much.
You need to remember that money is not the only way that a deal can be struck.Platinum could have just as easily offered a smaller cut in other projects in exchange on the IP control.For example, instead of a 60% - 40% cut into the next Astral Chain game(in terms of profit), they could have negociated something closer to 70% - 30%.Given the game success, and since Wonderful 101 was a bomb and is seemingly a dead weight to Nintendo, it could be advantageous for Nintendo to make that deal.
Other thing that is also important to consider is that Platinum is important to Nintendo.Or rather, that they both have a good relationship.Since they made a game that was successful on the Swicth(Astral Chain), are developing Bayonetta 3(With the port of Bayonetta 2 also doing seemingly well) and who knows what else, it stands to reason that it would be wise for Nintendo to keep Platinum happy and make a deal that, while good, would favor them more.
Just to throw some ideas around.