Person doesn't show up as a Model that you can use

(Bug, To be Fixed , Priority: Medium, Test Status: No automated tests yet , Reported By Justin du Coeur, )
Editor, Users and Identity
Summary: In particular, it doesn't show up in the Model Selector dialog, so there is currently no way to change a Person to a subclass. Since that's a useful feature, we should get it working again.
The actual bug is straightforward: since Person doesn't have Instance Properties, it doesn't get listed. Fixing it is easy.
However, fixing this reveals a much more bizarre knock-on bug: if you instance-edit a Person record, the Advanced Edit button doesn't work! It doesn't show as clickable, and it isn't. This is deeply mysterious, and I haven't yet figured out what's going on. It must get fixed.
Also, we really don't want Person showing up in the Model Selector routinely -- this is an extremely advanced and slightly dangerous feature. There should be a specific way to subclass Person, and to assign Members to it, rather than being so ad-hoc.