Eh, well, not quite. I can see where that interpretation might have come from, but I'd had ~15 years of dealing with the Linux community at that point, so I don't think inexperience can really factor into it ;)

What was really going on with that particular patch posting burst and the resulting, er, discussion was to try and draw some more developer attention, since - as you say - I really was operating solo at that point. Various companies had promised resources (ie people), but nothing was actually forthcoming. In the unlikely event that that particular patchset was accepted it would have been moot, but the real purpose was to highlight how much still needed to be done and to get people to publically express interest in getting dom0 into mainline, ideally backed by action/resources.

And while the feedback from the Linux community was strong and somewhat negative, it also put on record what form an acceptable upstreaming path would take.

The outcome was
  - the Xen/dom0 ABI needed to be refined, since the original one required some pretty unpleasant kernel changes, and didn't really make much sense
  - I needed to come up with a new, much more incremental dom0 upstreaming strategy

For the second, I did this by making sure that each patch supporting dom0 functionality also had at least some other purpose (many to do with pv-hvm), so there wasn't the perception of an endless stream of "not yet useful patches" (which is frowned upon). It ended up being so incremental that the "can boot as dom0" milestone (2.6.37) came as a complete surprise even to people within the Xen community.

And of course, I got a big boost when Konrad from Oracle and Ian and Stefano from Citrix started contributing a significant amount of time to the dom0 effort, taking over responsibility for getting large chunks of functionality into upstreamable form. Their help really tipped it from being a endless slog into an achievable goal.

On the contrary, the Xen and dom0 kernel versions are largely decoupled. There was a kernel/xen ABI extension added in Xen 3.4 which all the upstream (and post-2.6.32 xen.org) dom0 kernels require, but aside from that there's no coupling.

However, Xen and the usermode toolstack *do* need to have matched versions. You can probably get away with a bit of leeway between them, but the ABI is not considered stable.

I have no idea what changes Sun made to Xen to do their Solaris dom0 work, and I don't know if it's supposed to work on stock xen.org Xen - but if it is, it should work so long as the usermode toolstack is also updated.