If DX12 is as amazing as it's hyped up to be and truly a next generational leap in regards to power distribution, I can't see OpenGL being that attractive going forward.
I'm curious to see if DX12 blows away competition, will the enthusiasts knowingly not upgrade to Windows 8 or 9 (I don't think full support is coming to Windows 7). Will enthusiasts try to downplay the improvements in an attempt at making excuses for why SteamOS is the more attractive route? For all the hate that Microsoft gets because of Metro, if DX12 truly does impact performance like they're claiming, I can't see the gaming world's excuses being sound.
I also think the Universal App approach, including the XB1 support as being another potential driving force for DX12 to succeed. Which brings up a question I had. How does DX12 impact the PS4? From what I understand, they went with OpenGL and wrote a wrapper for DX 11.1 features. Would the PS4 be given the full benefit of DX12 like how XB1 will or is Sony resigned to getting a half assed version? To me, that could be very impactful since the PS4 is currently selling more and may be the lead platform going forward.