Are strange encodings used? My browser shows like ... 5% gibberish at the threadstarter's post.
Anyway. I remember that drag-and-drop was somewhat doable with ruby-gtk, and that was back in gtk2. I am not familiar with gtk3 but I guess it must exist for gtk3 as well.
I never tried to drag tabs between different INSTANCES of a program, but I believe this should also be possible in theory. Do we know of any program that does that? Perhaps there is already code for that which just could be tweaked to achieve that.