The only thing standing in Vulkan's way is developer support for it really, and since it pretty much supports all OSes, and is even supported in both AMD and Nvidia drivers since 2/16/16, there's no reason for them not to anymore (at least the large teams anyway).
Doom 2016 showed very good results with Vulkan. Yeah the game has an occasional freezing issue, but smart devs will know that's not Vulkan's fault, because it happens whether using OpenGl or Vulkan. I've also read recently that it's really only an issue on older model AMD cards too.
The way I see this playing out, is a lot of big budget AAA games will soon support Vulkan. That is because Vulkan requires a MUCH bigger learning curve than other APIs, so it takes an experienced team with lots of programmers to make using it worthwhile.
Some are feeling that also means Vulkan will give Linux/SteamOS a chance to catch up to Windows game library, but there's nothing to support that. If anything, Valve's already had a hard enough time getting Linux converted games to run as well as their Windows versions (usually they don't), so SteamOS/Steam Box interest has waned in the process.
Plus MS are really talking more in terms of console/PC compatibility, including Scorpio spec that will render it as powerful as a 980 Ti, with KB/M support. It would have been hard to imagine at the launch of original Xone, that MS would be better poised today than Valve to support forward thinking PC gaming, but they really are.
Bottom line, the future looks bright for Vulkan, and even might change Nvidia's GPU architecture once it catches hold, which is very likely given that AMD currently holds a lock on console APUs. But Linux's future, not so much, and largely due to Valve not doing well with SteamOS games.
Now granted, I know it's harder to get Windows games converted to Linux to perform well, than it is when giving them Linux support at launch, but I'm really talking about the fact that most gamer's have been negatively influenced by poor performing SteamOS games.
Thus I feel most devs will consider it too much a risk to put time and money into Linux support, because most gamers won't trust it to play well. It doesn't matter if SteamOS is free, it only matters whether devs feel it's worth their dev time, and I don't think most will.
Forget about Windows games converted to SteamOS though. Clearly Valve is fighting a losing battle on that, and that more than anything is what's all but rendered SteamOS and Steam Box meaningless in the gaming world. Then there's trying to keep up on Linux driver support, which is a battle in itself.