To be honest, i dont have a need even for that 280 and i know radeon work fine most of the time on most other chips, but i also know most people simply does not need dedicated cards so nothing more then Kabini/Kaveri . And i tend to think those APUs are best supported in the opensource driver .
That said most gamers will likely want to have anything with GDDR5 memory, that is enough. Next step are cards with more shaders and bus width 256/384/512.
So this HAWAII is nothing but BONAIRE as i understand, but with more shaders and 512 bus width... so i don't see a single reason (other than these techincal problems in driver development) to not supporting it . Who knows, maybe this has something to do with not so common 512 bus width on Deskop GPUs, not sure if regs/firmwares need to handle that somehow .