As far as I'm aware there isnt any blkfront support in the recent changes, which would be needed for EBS.
Support for blkfront is not needed to get up and running with Xen though, so it makes sense to defer it until later and get the bootstrap going and then the devs can focus on the remaining pieces.
I've only read a couple of pages of the tutorial over my lunch break but it reads well, looking forward to finding some time to dig through the rest of it.
I've been writing a ton of stuff in Gauche lately and I've found the experience to be great. The standard library is well thought out and the documentation is solid (aside from the ffi / c generator but that side of things seems to be still evolving).
Support for blkfront is not needed to get up and running with Xen though, so it makes sense to defer it until later and get the bootstrap going and then the devs can focus on the remaining pieces.