I have completed some preliminary technical research, and it seems that simply plugging USB to USB on two separate systems is a bad idea.
The short version is that USB 2.0 requires special hardware and know-how, and USB 3.0 requires only the fancy know-how to prevent directly connecting two systems via USB from frying the USB controllers on both systems. For our application, this could be made possible, but it would require Purism’s involvement or that of some people working very closely with them.
If I am wrong about this, please let me know. USB sync is still the most desirable for me. This seems to be the case for some others as well based off of some replies on this thread.
Worry not! Additional research shows that SSH in some form may be an option. This will require a network sync as far as I can tell so far, which I do not like – but if it is all local, I can live with it.
What I have now begun work on is a script that uses SSHFS to mount the phone to the laptop (from my T430 to L15 for testing purposes). Once connected, it will compare/contrast the PIM databases from both systems and offer the sync options. To start, it will probobly be basic, offering only to overwrite the older databases with the more recently modified ones. I have some learning to do, but hope to bring per-record compare/contrast and syncing capabilities. Once proper PIM syncing is in place, I hope to introduce file syncing: the main folders in the home folder: Documents, Pictures, etc.
This will be compatible only with GNOME PIM applications to start, as this is the preferred DE for Purism. KDE stores it’s PIM data in a different location and format.
I’ll keep y’all updated as things move along. I’m a full-time dad, husband, and employee, so it will take some time – but I am confident I will be able to get something working!