If they decide to take a more pro-consumer approach in the future and release the game on other platforms (GOG, Steam etc) I will happily pick it up as I am definitely interested in the game.
It is coming to Steam though, it will be after it gets out of Early Acess and more expensive naturally, but it will be there.
As for Epic Games Store, Supergiant entered pretty damn early on as a timed exclusive, that was one of the first if not the first exclusive on the shop so they didn't know what PC gamers would think, particularly because other launchers have exclusives or had timed exclusives as well, and Epic hadn't gone on to get crowdfunded projects like Phoenix Point yet.
They had no way of knowing the reputation that EGS would get and how many people would hate it or how much the opinion would be split regarding the store, nor other controversies, but it's done, they are a timed exclusive, they have said that the game will only be on Epic until it gets out of Early Acess, and it will continue to be the case.
Now, i hate Epic Games Store, aside from the cut for developers, i don't think it's done anything to help the game's industry, if anything else, it only had effects that i absolutely hate while the store limits the ability to purchase games for many people and ignores Linux users, so far i really can't say i like the store at all, BUT, Supergiant make great games, i have gladly bought and played Bastion, Transistor and Pyre(even if that was the game i liked the least, sorry) and thus i would say it wouldn't be so bad to get the game at Epic, hell, it's the only game i am considering getting(i just don't care for Epic that much and already have a big enough backlog that i can wait for games to stop being exclusives) on Epic.