I doubt they have the balls to not sell future Metro titles on PC. They've already released the generic "the views of this employee do not reflect the views of the company" statement like a day later after that dev made that forum post.
PC is their biggest platform from what I understand, mostly because fans of the S.T.A.L.K.E.R. series have latched onto it since it's the next best thing until a new game in that series comes out. I think a lot of people are going to boycott it, since there are a lot of people on the same side I'm on - if your game isn't on Steam, probably not going to buy it. Possible hot take, but I predict the next Metro game will have no timed exclusivity, and will come out on both Steam and the Epic Games store.