I think most speculation about 2 GB of RAM comes from the fact that it has a higher resolution display. That doesn't necessarily mean it will require more RAM, but it definitely would help.
I don't care about specs as long as the user experience remains great. There have been times when Apple released products that were hindered by underperforming hardware. One example that comes to mind is the iPad 3, which had a retina display but did not have the hardware to perform well with it. I still have one of these and it lags and stutters a great deal, as well as force closing apps often (even after a full reset).
I think examples like that are minimal, so let's hope the iPhone 6 Plus is not one of them. I won't deny that I'm a bit concerned about RAM and perhaps the scaling required for the 1080p screen. But for now, I will give Apple the benefit of the doubt and hope for the best. If not, then it'll go back and I'll get the smaller one.