Hi,
If you use tag based TOC there's an easy workaround. ... Just create a tag pill like eg: <<tag HelloThere>>
If you click it, you'll get a dropdown. This dropdown is drag & drop-able. If you change order there, it will modify the "list-field in the HelloThere tiddler, which in turn is used to sort the tagged list.
If you want to change order often, there should be a permanent solution.
But IMO this is a fast "hack"
have fun!
mario