Comments from community:

1)
The client-side C bindings are in tools/libxen.  Much of the work will be in 
xend of course, which is the Python bits.

2) 
I'm looking into xen api code these days and actually did small bugfixes mostly for xm-on-xenapi part.
Below is a 'TODO' list I personally gathered so far from the spec, the souce code and testing.
Though I won't participate in the meeting, I'd be glad if you find it useful for the discussion.

*** Virtual framebuffer support
     There is no way to set up vfb for pv domains.

*** PCI device passthrough support
     There is 'PCI_bus' parameter in VM class to set up
     PCI device assignment, but it doesn't work now.
     Also it would be desireble to make it possible
     that remote client retrieves physical PCI device
     information and assign one to a VM.
     (I'm now planning to develop this feature first.)

*   VM configuration
     We cannot configure 'cpus', 'boot', 'kermaps', 'usb'
     or 'usbdevice' (or maybe more parameters) through
     xen api.

*   VIF configuration
     We cannot configure 'model', 'accel', 'rate', 'ip'
     or 'script' through xen api.

There are more things that is to be completed or to be added, of course.

Thanks,
-----------------------
Yosuke Iwamatsu
NEC Corporation