OK, here's my list and a few you already know, I think.
1. Set the default tab
2. Order the tabs
3. Add some header text above the entire comment block - the reason I mention this is alot of people won't know what to do when faced with multiple options and likely leave without a comment.
4. Perhaps ability to add a Label under the tab icon - some people aren't as clued up to what the mean - it's true, we're not all Social Butterflies :)
5. Would be nice to highlight the tab icons with recognisable colours and colour draws the eye's attention i.e. easier to identify Google+ by Red, FB by Blue, Disqus ... maybe that's Light Blue, WordPress and Trackback I have no idea but you see what I am trying to say? Even an option to do this might be better so Minimalists can keep it like it is now. Though if you're using GenericIcons or whatever those Vector Icon Doodads are called then I think you can just style the colour using CSS, yes?
That's it for me now :)