Currently the site choice of question migration is only limited to 5 or 6 sites:
This is extremely underserving, because as now SE has a lot more niche sites, I can't imagine why we can't offer more site migration option.
I don't mean to clutter the Close Question Form UI with a lot more choices, what I mean is, can SO implements an algorithm that selects the best few sites for migration purpose? You can use either tags, or content context to determine what are the most suitable suites a question can be migrated to.
This should be a fun and interesting AI project work on, and at the end of the day, the programmer can gradually fine tune their algorithms so that more and more off-topic questions get migrated to their correct sites.