1) The XML that VI is using for the skins isn't very kosher. There is no DTD defining the language. They appear to be using a namespace that is defined from within their program.
2) VI has already stated that this is a Beta. This means that whatever editor anyone writes right now, might not work with next week's version of SIDL.
3) IMHO, I think that VI should have simply used the skin language that was incorporated for the patch program. Read those files - they make sense.
I would be more than happy to code up a UI editor at some point, but before I do, I'd really like to see where VI is going with this and how much functionality is being added. Furthermore, I'd like to see DTDs implemented and a better documentation of how the client interfaces with these files (ie, what values does the client look for and what values can we get from the client)
At any rate, I suspect that the net will be flooded with editors in the near future, assuming more users are curious enough to tinker with their interface!