> I'm yet to figure out (haven't searched enough yet) how to export the files out of the device (i.e. convert from their format to PDF/SVG) without using the USB web interface though; when I do, my workflow will be complete. 

My software does that: reMarkable Connection Utility (RCU). Paid, but GPLv3+, and works over USB or WiFi. It has a custom renderer that exports bitmap PDFs very close to what the screen shows--reMarkable's PDF export looks like a photocopy because they rotoscope a bitmap (why? dunno).

http://www.davisr.me/projects/rcu/