Plone itself does not provide WSGI based integration. It is using WSGI to integrate itself into a Web server. This means, the WSGI interface it before Plone (not inside Plone).
By default, Plone 5.2 comes with the "waitress" Web server and uses its WSGI interface. You may try to find out whether "waitress" supports several (so called) applications in the same process and how this is configured.