My 580 hasn’t arrived yet, so I can’t say this from 1st hand experience, but recovery mode should work.
The base system (with drivers) is traditionally loaded and therefore should bring a graphical interface. There’s no way I can see Apple releasing the OS without a useable recovery mode for ALL users.
I can test that it’s there, but my current card has an EFI so there’s little point (other than proof of existence).
I’ll try in a few days... BTW, I’m sure you know already that recovery mode will let you set the startup disk too. So in a pinch, you could use this as a boot picker screen too (a slow one however).