Yeap i've talked to itchyny quite a lot about various changes
https://github.com/itchyny/gojq/issues/153 and also upstreamed quite a lot
https://github.com/itchyny/gojq/issues?q=author%3Awader like custom iterators (to allow eval, own iterators and "empty" functions), query marshalling (query rewrite tricks) and a bunch of small things and bug fixes. But the largest change to add a JQValue interface is quite complex, other changes like extended literals is also a bit tricky.
Hmm weird list of changes for https://github.com/wader/gojq/compare/fq...itchyny:gojq:main but i guess it is because i haven't kept my main branch in sync. The fq branch should be based on latest gojq/main as of now. I usually try to rebase as quick as possible.
Let me know if you have any other questions or want to help out! maybe email etc as i usually don't check HN comments replies that often :)