How to migrate users with custom fields from plone 4.x to 5?

Hi I have developed an add-on for plone 4.3 similar to and want to migrate an existing plone site from plone 4.3 to plone 5. The migration implies to modify the userdata add-on substantialy. The old add-on registers an utility for that no longer exists on plone 5.

How should I accomplish the migration? Any examples?
Must I uninstall the utility before changing the zodb to plone 5?
Or create a mockup class for IUserDataSchemaProvider?

I'm facing this too.

Unless someone else knows how to work around it, I'll bang my head against it for awhile and let you know if I make any progress.