The bigger question to me, is how would game developers
on the PC market (OSX/Linux included) would scale their
games? You would need different assets (level of detail?
mip-mapped texture levels? meshes?) - but tuning this to
work flawlessly on many different configurations is
hard...
This isn't really any different from what it has been until now. All AAA games have different levels of detail for meshes/textures/post-processing etc. Even when not exposed to the user as options in a menu these different levels of detail exist to speed up rendering of for example distant objects or shadows where less detail is needed. DX12/Vulkan is not going to change anything in that regard.
Doing a good PC port is not as easy as it may seem at first glance. Different hardware setups and little control over the system cause lots of different concerns that simply don't exist on consoles, which means nobody bothered taking that into account when the game was originally built. These new APIs will help though; the slow draw calls on PC are a pain compared to lightning fast APIs on consoles (even Xbo360/PS3!).
Doing a good PC port is not as easy as it may seem at first glance. Different hardware setups and little control over the system cause lots of different concerns that simply don't exist on consoles, which means nobody bothered taking that into account when the game was originally built. These new APIs will help though; the slow draw calls on PC are a pain compared to lightning fast APIs on consoles (even Xbo360/PS3!).