AM4 implies it may be suitable for FX Processors, if the socket is backwards compatible.
More likely to be FM4 at this stage and low power.
I suspect the different sockets depends on the number of DRAM channels and PCI-E lanes, since "Xen" CPUs will have the PCI-E root complex on the CPU instead of the "north bridge", so more lanes means more pins (unless you're using a PLX bridge chip of course.) I suspect Xen's architecture will end up on most of AMD's CPUs if it proves to be a success. What I'm seeing is the same thing Intel is doing; skt1150, Intel's mainstream platform, goes up to quad core, sports an iGPU, and supports 2 memory channels, which sounds
exactly like AMD's APU lineup (albeit slower CPUs, but same general idea.) Then you have skt2011-3, Intel's HEDT and server platform, spots 40 PCI-E lanes instead of 16 (which requires over twice as many pins as skt1150,), you have quad-channel memory (which doubles the number of pins associated with DRAM), and you have bigger dies that can consume more power so you add pins for power delivery. So you have this situation where skt2011-3 by virtue almost twice as many pins as 1150 because it can have twice of just about everything (sans the iGPU, which really doesn't take much pinning.)
So with that said:
If FM4 is to 1150, then AM4 is to 2011-3.
I say this because if "Xen" is claimed to have a huge number of PCI-E lanes
on chip, then I suspect that AM4 will have a very different pinning than we've seen in the past which wouldn't jive nicely with how APUs have had a limited number of PCI-E lanes (22 on FM4 coming up I think). The simple point really is that this is AMD (like Intel) making a distinction between the consumer products and the high-end/server market products. They've really just tuned the lineup with the market in my opinion. More pins = more traces = more money and there is no need to make a mainstream platform expensive if the company is considering their bottom line.
It really comes down to market segmentation. Generally speaking, consumers will be happy with an iGPU and fast cores... and generally speaking, servers and workstations will require either discrete graphics or none at all (minus something super low power and weak) and more cores. But either way, Xen (if half decent,) will find its way into both markets like Bulldozer did. I think that's a given.