I never really got a clear sense of how such a merge would be carried out. Merging the codebases looked to be quite challenging technically, since despite the outward UI similarities, they were implemented considerably differently.
So perhaps it would be easier to use the Xara source as a spec. on how to make a certain functionality?
Merging the *projects* (the human element) looked even more challenging, and didn't really get much discussion.
Inkscape is a very community-driven, community-owned project, with decisions made bottom-up through merit and hard work; this sort of structure encourages and incentivizes volunteers. Xara is a more traditional corporate entity, with decisions and directions driven top-down by the management; this type of structure can be less appealing to volunteers (especially ones accustomed to the more free approaches of projects like Inkscape). Fitting those two organizational philosophies together without completely ruining the result would be a major, major achievement.
I got the understanding that Xara would not interfere with the Inkscape community or how Inkscape works (code wise). Xara would then implement the functionality that they felt were important in the case where the community prioritized feature X over feature Y.
Isn't Cairo superior?
It is, although not for the reasons you might expect. With renderers, people often look at the performance and mathematical correctness as the primary measures. At the time Xara was looking at it, they claimed that their engine was much, much faster than Cairo; cworth was very interested in this, but could never get the benchmarks from them to verify their results. So we don't know if they were using a recent or old version of Cairo, what sorts of optimizations were done, etc. As well, cworth began a long program of focusing on performance starting about that point, and it's possible that today he's closed that gap. It's impossible to say, however, without rerunning the tests; it's conceivable Xara could still rank better on those benchmarks.
Today I looked at the splash sceens for 0.46, and that was the first time ever I felt that Inkscape wasn't crisp in regards to speed on my 2GHz AMD64 and onboard nForce6 GPU.
But the real reason why Cairo is superior is because it is a widely adopted renderer that's integrated into and supported by the Open Source community as a whole. Using Cairo means you benefit from improvements made in it, and means that you're more likely to remain compatible with other Open Source programs.
Yes, it's beautiful that e.g. Mozilla choose Cairo for Firefox 3. I would assume that means they commit patches back to Cairo rather than doing workarounds in Firefox 3.
I don't know of one, but would expect their website to carry it if it is available anywhere.
I have started a thread at Talk Graphics Forum, so let's see what that brings. Otherwise that could be a Google SoC project to sort out the functions from Xara? =)
One thing I definitely would like to see is importing of Xara files.
What would it take to implement that? Copy/paste from Xara source, or write loader from scratch?