No laptop is ever future proof, especially if you want to play games. For that matter, no portable laptop is actually any good at playing games.
That’s the reason I replaced mine with an iPad + Desktop PC last March, for less than half the price of a top spec MacBook Pro. The iPad is far more portable, even than the 11″ MacBook Air, has significantly better battery life than any of Apple’s laptops, is much better suited to reading, and is far cheaper to upgrade on a yearly basis.
The desktop PC I built is has an overclocked 2500K and GTX 570 in it, an will run just about anything in 1080p at a solid 60fps (no framerate drops/stutters) even the latest games. Desktop app performance is still faster than any machine Apple sells today.
I do miss OS X though, and once (if!) they update the Mac Pros to use modern hardware again, I will probably buy one to get back to it.
All that said, if it’s a laptop you want, keep the Retina MacBook Pro. There’s nothing better today, and you will regret it once more apps are updated with retina support. If you really plan on keeping it until 2016, who cares what the state of retina updates are now? You’re going to be on the leading edge of updates, and I bet most of your important apps will be updated long before the new Retina MacBook Pros are introduced.
And yes, it’s going to start feeling slow by then, but any laptop will. It’s an especially bad time to buy one for gaming, as next year the new consoles will be out and hardware requirements for games will go up considerably. (Even if you buy a laptop next year, it will struggle with them)
The only reason to buy a PC notebook, is either because you don't care about weight, size, heat, noise, build quality, or battery life, and want a fast “gaming” laptop (which will still be out of date in a year) or because you want something cheaper that you’re happier about replacing in a year or so.
Personally I’d still recommend buying the Retina MacBook Pro, selling it and upgrading in a year or two instead, or buying a gaming PC that will last, and a properly mobile laptop/tablet. After having a couple of iPads now, I couldn't go back to any notebook as they have about half the battery life at best, regardless of what the advertised times are.