16-24GB is, for me, stupid. Standard builds come with 2-4GB at the moment. Going by the Best Sellers at dixons.co.uk (a pretty prominent seller in the UK for Joe Average), the best is 3GB and the second best is 2GB. Best Seller for gaming specific section of their site reads up at 6GB, and that's a £1,600 desktop which is insanely expensive to all but the best paid people out there.

If you're going for a custom build, I've not seen anything with 16-24GB out there. I can sort of understand some might go for 8GB or something, but what the hell would you need 16-24GB RAM to run?

If the game is coming out at the end of the year, I'd expect 4GB to be used in less than half of the desktops that are in use throughout the world. For gaming PCs, it'll probably be about standard issue.