4K gaming is a thing, just not one I'm interested in, but it's there for those who have the money for it. Just make sure that if you ever go for it to have a 4K compatible monitor as most models cap at 1920x1080.
Andy's. My next rig will be similar to his, you really don't need to shoot for so high in the market unless you're looking to become an elitist. When you break the $2,000 barrier you're entering the pointless overkill territory.
Tsuyu's rig is a monster, but based on the parts it looks under $2,000 for the time, but I might be wrong (you can always ask him).
If you
really want to go higher though, then replace Andy's parts for GPU, CPU, and Mobo for:
GTX 980
Intel
i7-4790K (if you plan to overclock, look into liquid cooling)
Maximus VII Formula (just a fancier VII Hero, but it does have metal plating)
There's 6 & 8-core CPUs available right now (for appropriate mobos), but the performance gain for gaming doesn't justify the price-tag (and likely won't for a number of years). They're useful for video editing projects though, otherwise I wouldn't concern yourself over them.
Trust me, it's never the wrong time to start building a PC. Gaming tech is a forever evolving beast that has gone at this pace for many decades, it's nothing new. I've had the same rig since 2010 with only one upgrade to my GPU, it was built on a budget around $600. I'll be making the switch to a new build (Intel/nVidia based) sometime next year when I get the money all sorted. As it stands though, my rig is still fine and can still max out a number of the new games (Watch Dogs, Thief, Dying Light, MGSV, etc).
The misconception of upgrading every single year is a stigma that was created from PC elitists that strive to have the latest and greatest components, even when they don't even need them (that and people who don't buy smartly). :/
I have to give credit where it's due though, the PS4 & XB1 are impressive for what they are. They'd never be able to market a console with the power of a GTX 980 and sell it for under $400... the GTX 970 alone is $330, and the 980 is $550.