Already got a reply:
The customizable Markdown export is only on its first iteration, so I will forward your feature request to our cofounders to discuss for future updates!
You’re actually one of the first to request an integration with Logseq. I’ve noted your request in our system, so as more users request the integration then it’ll move up in the queue to develop.
If you’re interested, I would suggest you reach out to them for an integration with us by sharing our API docs: Readwise API | Readwise. Our users have successfully convinced many apps to integrate with us already using this tactic!