git-bug is built to be portable - today, the way git-bug interacts with other platforms which do not support reading from its namespaces directly is through bridges.
right now, git-bug has built-in bridges for github, gitlab, and jira. i am working on the design for a more modular system in which bridges can be built by anybody and used as "plugins".
really, though, the better, long-term goal is to work with $PLATFORMS to have them update their issue tracker to use git-bug's issues (that is, read from and publish to the refs/bugs namespace using git-bug). there's a bit missing right now to make this easy, but it's something that's very much top of mind as i think about git-bug's future.
Imagine having repository issues seamlessly propagated and replicated across all your git mirrors.