Hi,
Quite a while ago, I modified tabbar.el to make it possible to reorder tabs.
Honestly, I never thought other people would like to try it, so I didn't
even bother to make it compatible as another emacs lisp file. I know it's a
poor exercise, but if you want to try it, I am attaching my modified version
of tabbar.el, and feel free to give it a try.
It's been a while, I can't remember every detail I made to the file, but I
believe tabbar automatically sorts tabs. In order to make reordering
possible, you have to disable the sorting routine. If you have time, you can
certainly investigate the changes I made, do whatever you want to it. :)