Invite users for creation

For the task of merging the user-registration addon into the Nuxeo core product, there are a few issues for which I would like to discuss with you.

Today, when using the user-registration addon, a document model UserRegistration is created. This document contains several informations related to the addon and the user information for the creation of the new user.
The schemas used are hard coded in the addon. We would like to change that and let the users the possibility of overriding the schema used to define a user (as it's done today for the regular creation of users). We will have a problem with the definition of the document type UserRegistration which includes a few "static" schemas used by the addon and the "dynamic" schema used to declare the user fields.

A solution proposed by Thierry is to use introspection on the user schema when the server starts and add it to the core-types-contrib defining the document type UserRegistration.