Since you said near future the question probably doesn't apply anymore, but I want to answer it to clarify the situation in case some people have the same doubt as you.
You shouldn't have any problems for that setup, whether the laptop was already bought with Windows 8 or not.
What you read about incompatibilities is probably related to a security feature of UEFI called Secure Boot which requires bootloaders (ideally anything accessing hardware directly) to be digitally signed so they can be verified, which among other things prevents malware targeting boot loaders or man-in-the-middle attacks when booting over the network.
For the Windows 8 certification (for new machines), Microsoft requires that feature to be implemented and enabled by default; so unsigned or compromised bootloaders wouldn't be able to boot by default. But, Microsoft also requires that the user should be able to disable that feature altogether if he want to (if the machine doesn't have an ARM processor), with it disabled everything would work as usual.
Anyway, many systems with UEFI that didn't ship with Windows 8 don't even implement Secure Boot, so it's even less hassle.
The problem may be when you want to have Secure Boot enabled but also compile your own bootloader or kernel. In that case all that's you'd need to sign them (maybe only the bootloader) and add the public key to the UEFI storage so that anything signed with your private key would be verified as secure, but you'd have to buy the key to sign it.
Regarding what you say about Windows 8 booting faster, it won't cause any problem in that setup either. It's something they called hybrid boot which uses hibernation to cache most of the core system instead of a traditional boot sequence; but it happens in any kind of system not only UEFI based ones (remember that Windows 8 works in BIOS based systems as well).
In any case if that gives you any kind of problem it can be disabled too and the traditional startup is still available.
I hope that clarifies things.