If you're looking for something light, self-hostable and a bit more "social" (i.e. with pull requests and bug creation from the web) I recommend looking at https://tangled.org It doesn't render perfectly in Dillo but basic features appear to work.
However I really like what you've done here for Dillo as well.
Yes, but all those services have the same main problem: a single point of failure. They also don't work offline.
I believe that storing the issues in plain text in git repositories synced across several git servers is more robust and future-proof, but time will tell.
Having a simple storage format allows me to later on export it to any other service if I change my mind.
That said I wish there was something a little better than cgit