Of course, the first question that comes to mind is whether this MMOG (notice the careful of absence of an "RP" anywhere in there) would be in the vein of S.T.A.L.K.E.R. with some massive elements added to it, or whether it would be a completely new side project. One also has to consider whether GSC is going to leverage their shiny new Xbox 360 SDKs in pursuit of this project, or whether it's going to be a PC-only affair. So many variables!
One thing is certain though -- GSC better have a pretty good idea of what they're getting into, because the market for MMOs is beginning to look really crowded these days.