I did try something very similar and it works...for the most part.
- Using ESXi as your bare metal hypervisor, works just fine. The hardware support keeps becoming better.
- Running WHS 2011 as a VM under ESXi works just fine. Make sure you either passthrough your RAID card or native disks to it, for best performance.
- Running Windows 7 as a VM under ESXi works fine, but with some caveats. If you will also be using this VM to "watch" your content, you need to VGA passthrough a card to it. That sometimes works, sometimes doesn't. Depends on your hardware and the motherboard's slots, VT-d support in the CPU, and motherboard. You'll also need to passthrough a USB controller if you want to connect your IR receiver/keyboard/mouse to the VM. This usually works fine. (Tip: Physically identify and mark the USB ports on the backpanel that are passed through....
- Connecting a Windows 7 VM to a HDHR on the network works just fine.
- You do need to do the Digital Cable Adviser override hack for a virtualized Media Center to pass the Digital Cable Adviser.
- Using extenders with this HTPC VM works fine, but you may need to tweak you network configuration.
Edit: Oh, and a few other things.
- The M1015 passes through just fine to WHS 2011 in a VM under ESXi.
- Since you'll be doing a lot of passthroughs, do not use ESXi 5.1, it is buggy. Use a fully patched 5.0 Update 1.
- You don't necessarily have to use local disks in your W7 VM to record TV, since your W7 VM and the WHS 2011 are on the same ESXi server. W7 can be hacked/told to record to a network location, but this usually is buggy when you're using physical networking/gigabit due to a number of reasons. But if you are running WHS and W7 as VMs under ESXi, the virtual network switch in ESXi operates at 10gbps, and recording to the WHS directly works fine. Very low latency with the ESXi switch and in fact may be better than passing disks to the W7 VM and recording locally and then moving them to the server.
- I don't know why you'd need XBMC for anything, unless you "want" to use XBMC for something.