BF4 will do fine with 3 GB, the question is games after that. It is hard to tell because current games being released are still only targeting a max of 3 GB because that is mostly what is on the market (Titans are a minority and the R9 290X has just been released), not to mention, making PC games look too good would hurt the current consoles, so I wouldn't be surprised to see a big jump in texture resolution in games released in the next year.
Some people will claim that the GPU will run out of horsepower before it can make use of more than 3 GB of VRAM, but I'm not so sure, because of the current status quo, and also take into consideration Mantle, which will make more of the raw horsepower available, so while some things may be true while rendering in Direct X, it may not be true using Mantle.
I understand what you are saying. Appreciate it. I wish the 780ti was 4GB, it would make my decision much easier. Maybe some more info will leak and get confirmed so I can make a better decision.