When the Banktivity mobile app sees a Banktivity desktop file (.banktivity7) it reads right into the file structure rather than seeing the .banktivity7 as a single file; it does the same thing as .zip, where open dialog will tear right into the contents of the .zip rather that recognizing .zip as a file itself.
Presume there is a hack (probably an easy one) where Banktivity for iOS could read/write to the Banktivity 7 file