Great idea, could incorporate into x-marks? Rated 5 out of 5 stars
My work requires reading many scientific & engineering papers; this add-on essentially allows me to treat online articles as PDF papers, by allowing commented highlighting.
The only tangible improvement, IMO, would be to find a way to export/serialize the bookmarks into a quick script, and allow easy exports.
As previously mentioned, Google support or even X-Marks would be ideal, but synching could honestly be as simple as copying a flat-file of entries into foreign profile directories.