Monitors aren't really the problem though it's the fact that the dual 780ti's you'd want is a good £1000 before you even consider anything else and it's not like you can throw those into a budget rig or skimp on cooling.
It's nice but it's still niche. No one has any doubt about it in the future but right now the cost for the performance doesn't add up for the majority.
No one is going to want 780Ti's for 4k gaming. The Maxwell and Volta series and beyond will be much better suited for higher resolutions. Even the middle tier cards.
I'd say GPUs are even ahead of monitors if nvidia can keep to their schedule.. At worst they are right in line with them