It's not “easy”, but we've found that because it's based on a declarative DSL it's less effort than you might expect. And we're finding that there are common patterns that you use in your graph construction rules, because there are many aspects of name binding that end up working the same way in different languages. So, hand-wavily (not out of secrecy but because of not having rigorous data yet), we're finding that it's O(months) to get a new language out the door.

We do have a couple of other languages in the pipeline that my team has been working on, both in terms of writing stack graph rules to get precise support, and also to write "fuzzy" tagging rules to get search-based support. And we definitely do plan to include lower level languages like the ones you mentioned.

Lastly, one major reason that we're doing all of this in open-source projects is that we want to ensure that language communities can self-serve support for their languages, should they wish to. That will be especially useful for the long tail of languages that my team will honestly never be able to get to ourselves. We have some work to do to get the documentation written to properly support self-serve stack graph rules, but it's definitely a goal that we're aiming for.