No, not interchangeable..
http://vr-zone.com/articles/intel-core-i7-ivy-bridge-e-core-i3-haswell-lineup-detailed/37832.html/3
* LGA 2011-3 and LGA 2011 share the same physical processor dimensions of 58.5 x 51.0mm
* LGA 2011-3 and LGA 2011 share the same ball pattern pitch of 1.016mm, hexagonal shape) (this refers to the little circles on the CPU itself which pins on the motherboard socket make contact with)
* LGA 2011-3 CPUs are keyed differently than LGA 2011 CPUs, meaning you cannot use a LGA 2011 CPU in a LGA 2011-3 socket, nor vice-versa
So in summary, despite the first two similarities, LGA 2011-3 and LGA 2011 are not interchangeable. Thus if upgrading to an LGA 2011-3 motherboard, you will need to buy an LGA 2011-3 CPU.
Nice features tho..
http://vr-zone.com/articles/intel-core-i7-ivy-bridge-e-core-i3-haswell-lineup-detailed/37832.html/2
Wellsburg Chipset
With Haswell-E, Intel will introduce their new Wellsburg family of motherboard chipsets. The biggest new feature (and its really big) is the support for DDR4 RAM clocked up to 2133 MHz (of course, you can overclock and take it much further than that). The Wellsburg X-PCH will support a number of connectivity options:
Up to 6 x USB 3.0 ports
Up to 8 x USB 2.0 ports
Up to 10 x SATA 6 Gbps ports
Integrated Clock support