Windows 8 support and GPT support have nothing to do with each other.
Boot Camp will be updated with drivers for Win8, it will never be re-written to support GPT.
I wouldn't say never:
Apple's support article say "iMac (27-inch, Late 2012) computers do not support installing Windows on the 3TB hard drive
at this time." (emphasis added)
Sounds like they're trying to send the message that this lack of support isn't a forever thing.
In order to support 3TB hard drives with Boot Camp, you need to use a version of Windows that supports GPT -- that means a 64-bit version, running in EFI mode. The EFI mode is what's lacking.
People have been trying to hack together ways to get that, but they run into problems due to a combination of bugs/limitations both in Apple's EFI implementations and the EFI-mode boot code in Windows.
If Apple makes an EFI update that's Windows-friendly, it should be relatively straightforward for them to support GPT with Boot Camp. And if I had to guess, I'd say the likeliest time to release such an update would be to bundle it with the Boot Camp update for Windows 8 support (although you're right, they don't actually have anything to do with each other).
Realistically, this is bound to happen sooner or later -- storage isn't getting any smaller and Windows is slowly moving towards EFI/GPT being standard, so if Apple wants to keep Boot Camp as a viable feature, it
needs to support Windows in EFI mode with GPT partitions.