Are you already running Plone 5.2 with Python 3, or are you still on Python 2?
If you are already running on Python3 and have no more Archetypes in the site, then there is data migration wise not much to do for Plone 6 and as @petschki responded there is a Plone 6 branch of plone.app.mosaic (that needs more work).
The possible challenge with PersistentTiles is that their data is stored as an annotion on every context/item and the annotion is loosely coupled through the content layout html field with urls containing an Annotion UUID. I assume (but have not tested personally) that with the inplace migration method those annotations will be saved / restored.
If you want to use a different migration strategy (ETL with transmogrifier or collective.exportimport), I know that at least for collective.exportimport there is no support yet for those Annotations from PersistentTiles.
We have done some first work for a customer this autumn to allow for copying mosaic layouts from one site to another by extending collective.exportimport, but there are still some limitation and issues to solve there. I'm not knowledgable on the current support in transmogrifier setups or pipelines.