I run 9front in virtualbox, and, while I totally agree that its a waste of time to test it because they *always* break something in vbox, you're pretty safe if you stay on the 4.3 series and 5.0 series (on my end: 4.3 on freebsd is tested and 5.0 on windows is tested). I know you don't get the latest and greatest features, but it works and you can get your work done which is more important than features. If you want to try fixing things, I'm sure the patches would be accepted, but I don't think you should unless you have *very* good reasons to because of how terrible virtualbox is.
-- Veety
