This isn't a very exciting change, and probably won't even be particularly useful until the site is publicly-visible, but I've now set up the https://tild.es domain to handle shortened links to topics and groups.
The short link for each topic is available at the top of its sidebar. For example, this topic's is: https://tild.es/9au
It also supports linking to groups, like https://tild.es/~games (not actually being used anywhere on the site yet)
I'll probably also add support for linking to comments and users eventually (maybe via
tild.es/u/ respectively?). Please let me know if you have any other ideas of what might be good to do with it, or if you notice any issues.