Guys, it's been already discussed before, here's again the recap:
- perpetual license will be gone IN NO TIME, since, as stated by Adobe in their blog, they are already working on incorporating Substance in CC. This is no speculation, it's already happening, we are talking about months. Steam will follow, there is absolutely no reason to think Adobe will behave different just because is Substance (see Mixamo/Fuse). Everything is tied to CC, so forget about anything on Steam.
- forget also about Linux, seriously, don't even ask. It doesn't exist any significant Adobe software CC, that is supported under any Linux distro. They have the money and the resource to do it in years, if it's not happening it's because linux userbase doesn't worth enough money, so they simply don't care. Again there is absolutely no reason for this to be any different just because is Substance.
- what Allegorithmic says from now on means nothing, they do what Adobe says. See the new logo on top right of this page? It says: Allegorithmic - An Adobe Company. This is not a merge or an equal deal, Adobe owns Allegorithmic, the resources, the know-how, the people and everything else.
- forget about your UDIM seamless paint or any significant updates for quite some time: all the resources will be dedicated to incorporate the software in the Adobe CC Suite for a quick transition. And after that, well, everybody knows how update works with Adobe, so don't hold your breath.
- even though we can buy perpetual right now, it's not sure what will happen, they can change the license tos whenever they want in the future.