I've introduced an experimental notion of attachments for types in the TypeInfo api.
This allows for easier caching of information related to a type.
It also means that when we introduce a better caching mechanism than the
WeakTypeCache we can control better what gets flushed from memory because
it is not being used.
My one concern is that this information is public so it would probably need
a security permission to allow modifcation.
Given that concern, it might be better to just use a more normal