6gb is not going to become the standard. 90% of games now are going to be developed to run on the new consoles as well as PC. So keep that in mind, developers are not going to make games that will not be able to be played on the new consoles, they will lose money, and that’s bad business. Another argument is why would they be releasing the 780 ti’s and 290x with 3-4gb of ram if they were going to be no good in a couple of years. Watchdogs uses allot of Vram but they have said it is poorly optimized and they are currently working on a patch to fix it. People say BF4 uses over 2gb of Vram, when actually it’s more like 1.8gb of Vram. DX12 going to be standard soon and it is going to optimize how your GPU uses the Vram bringing the requirements down as well. I am honestly getting tired of the whole Skyrim argument. I run Skyrim maxed out with a minimum of 46 mods (depending on how I am playing that day) on my laptop with a 2gb 770m, it runs just fine with no issues!
You only really need the extra Vram if you are running multiple monitors at high resolutions 1600+ for gaming. There are a few other reasons but I am not going to get into them all, rendering ect. If all you are doing is gaming you will be fine with 3-4gb of Vram for long enough to where you need a new GPU with more processing power before you are going to need that much Vram.