Yes, that's understandable, but that's exactly where Mer has an advantage. They explicitly separated the hardware adaptation bits from the rest of the system. I.e. hw adaptation is pluggable, and the rest of the core distribution stays the same (within the same arch like ARMv7, MIPS and etc.). Since putting all kind of wild mobile kernels differences in the mainline doesn't sound like a practically rapid approach, Mer just doesn't dictate it, and hw adaptations are up to the vendors to provide. It allows moving fast and be flexible with it.