Per https://github.com/harvesthq/chosen, jquery.chosen is deprecated. Can Select2 be added as a replacement? It has much of the same functionality, plus the appearance is much more in line with OOUI.
Topic on Talk:ResourceLoader/Core modules
Appearance
@Ahecht: We're probably going to want to drop it, rather than replace it; it's been unused in production code for a long while, except for any gadgets/scripts.