Hello Capet,
Mega.nz is already supported, they have now a sync-client to synchronize the data locally.
That means, you can use it already with Boxcryptor.
Download: http://megasync.en.lo4d.com/
The created sync-folder of Mega.nz may simply be set as a Boxcryptor Location afterwards.
https://www.boxcryptor.com/help/manage-cloud-providers-and-locations/
Since Mega.nz doesn't support "WebDAV" there's no possibility to use this cloud provider with Boxcryptor on mobile devices.
Kind regards,
Yasmin