My interpretation (and apologies if this is obvious to you) is that they will define certain interfaces between the driver and the outside world, and any manufa

My interpretation (and apologies if this is obvious to you) is that they will define certain interfaces between the driver and the outside world, and any manufacturer will be able to provide something (a library or a daemon, I guess) that implements those libraries. When they say "cross-platform use-cases", I think it means they want to make it easy to build the Mir driver and Android driver from the same source tree - and quite possibly the Windows and OS X driver too. So hopefully they will have some quite general interfaces. I think the ideal scenario is that the driver interface they define has a very general interface, and then there's a wrapper that turns that interface into an Android driver, another that turns it into a Wayland driver, another that turns it into an OS X driver, and so on. But I don't know if graphics drivers would accept the performance penalty of even a very thin wrapper.