I, for one, will assume a BIOS stopgap (you read it here first!). Simply because a stopgap would be (roughly) a quick implementation and potential retrofit for existing hardware. Switching completely over to an EFI-based solution would be the ideal, albeit more expensive, solution. Of course we have the chicken-and-egg problem once again... what Mobo manufacturer will switch ALL their boards to EFI without a drive that requires it? Who would buy a drive over 2TB that doesn't work on any PC (except on one Asus? mobo). Yes, Apple runs EFI and thus the "PC" qualification. Of course, they'd never sell a stock computer with 2TB+ hard drive space anyway. You're lucky they decided to up their drives to 640GB.
Next question would be, sure, the BIOS won't recognize the >2TB drive capacity (at least, anything above 2TB), but what about USB-attached drives? I would assume these drives would at least be usable as externals.