eh honestly i don't think extensions are really all that bad. it's a standard and extensible way for third parties to advance the API, and - presuming the extension is rationalized into the API appropriately - allows for clean evolution & progression.

on the other hand, i'm not so sure that i agree with the approach of advertising even basic functionality (e.g. swapchain) through extensions. i understand vulkan has uses outside of graphics. i think that could have been better exposed with hard profile boundaries or something..