I’ve done this on our instance, but we are left with an irritating (albeit relatively minor) problem: the user fields in the /review page are not ordered nicely as per @eviltrout’s good work in Custom User Field Enhancements . This means that the relevant info to decide 
or 
is buried for our moderators/admins.
It could be that we could just hack this for our instance (main admin is @pacharanero), but I suspect that this is actually an issue for any Discourse instances that mandate data entry on joining in order to decide / control who should join.