To everyone wondering, it’s still possible for the set to just be a normal set for everyone to earn, but it could still be only for steam players! (No way to tell yet)
I feel like it will be obtainable by linking your account to steam once the PC version launches, We'll have to see when that time comes though. I'm very excited.
Not much details are public at the moment! So it’s hard to say. But it could be free for PC players, but still earnable for mobile players. Or they will just add it as a set like normal so everyone has a chance on getting it.