IIRC, one reason that Archetypes is currently still a dependency of Products.membrane, is because Products.membrane installs its own catalog.
A catalog in Plone offers a way to search for items in the Plone database (ZODB, Zope Object DataBase) without ‘waking up’ all objects. The catalog has indexes, just like PostgreSQL or MySQL. The standard catalog in Plone is an object with the id ‘portal_catalog’. It is used heavily in Plone for building the navigation and of course for the search form.
Products.membrane uses its own catalog, with the id ‘membrane_tool’. This was originally done to avoid adding even more indexes to the already index-heavy portal_catalog.
Problem: whenever a user-as-content object gets changed, or added or deleted, all catalogs must be updated. For the portal_catalog this happens automatically. For all other catalogs, you currently need Archetypes. It has some code and configuration that allows you to say: “when an instance of this portal_type (some user-as-content type here) gets updated, Plone must inform this extra catalog as well (membrane_tool here).”
The consensus seems to be that it is better to put the extra indexes (and metadata) that Products.membrane needs, into the original portal_catalog. That would mean we can lose the dependency on Archetypes.
Yes, that is the idea.