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I would also donate for this, echoing what others said above (especially Brian Davis). With syncing, tab sets replace other bookmarking utilities, and now offline tab sets, current tab sets, and bookmarks are all rolled into one seamless tool in Tabs Outliner.

You could enable this option only if a one-time donation is given, as a suggestion. Using google drive ala tab cloud makes the most sense: I know many people who are afraid of tying their bookmarks to proprietary services that might shut down in a couple of years.

I'm a programmer who'd be happy to join the beta testing team to when it reaches that point...