I'm working on improving the usability of guides as a GSoC project.
My mentor (Johan), suggested that henceforth "inkscape:guide" be used instead of "sodipodi:guide" as the SVG attribute for representing guides. In my branch one of the things we worked on was to change the co-ordinate system used by guides from desktop co-ordinates to document co-ordinates.
Snapping, general guide operations etc. seem to be working properly after the co-ordinate change in my branch.
A problem arises when a user opens an SVG that has "sodipodi:guide" using a build of Inkscape that uses "inkscape:guide" as the attribute.
What should (ideally) happen in this situation?
Johan suggested the idea of creating an extension script that transforms between new and old guides. The user will be made aware of this extension when an incompatibility is detected.