Wow this is excellent, it looks like we were inspired by the same problem and had very similar solutions. I should've known a tool like this existed somewhere, I just didn't look hard enough :). Either way I'm pretty happy with the output of node-txr even if I could've used wormhole without needing to build it.
As of today the server could read all data, but I believe wouldn't be a huge lift to implement E2E encryption with SSH or PGP keys (or something similar).
If you want to look for inspiration from an established tool, check out wormhole. Their UX is extremely simple.
https://magic-wormhole.readthedocs.io/en/latest/welcome.html