Too be honest I just threw a random ram number out there lol. I don't know, I'm kind thinking we are going to need 8 gb ram, but that isn't going to happen, however with the obvious move to the cloud coming in the next few years you will only need to kit the machine out for 3-4 years....special perhaps 4gb would do it.
Even 4GB would be quite expensive, requiring 256bit membus opposed to 128bit (or could it be done with 128bit in clamshell mode? not quite sure really, but good luck fitting 16 memchips on the board)