Around Nov 2013, will I be able to get an 6-core Intel (non-extreme) "K processor" on some chipset other than x79 ... that is PCIe 3.0 certified?
yes (assuming IVB-E is out by then . . . which it is supposed to be . . .)
Will i7-3930K and i7-3970K only ever run on x79?
no, they should run on the new chipset . . . but they will still only be validated for PCIe v2.0
The Xeon workstation build is a nice pipe-dream but in reality, I need to keep it more "mainstream desktop"
You should probably forget about 6 cores.
A 4-core Haswell will beat a 6-core SB in most everything and never be far behind in anything