The value of firefox send for me was that
1) it was hosted
2) it was free
3) I trusted mozilla
As a developer, I am already aware of similar open-source packages like magic-wormhole. The code/tools themselves don't solve the problem, though. I had my non-techincal mom exchange sensitive documents through Send but I'm never going to get her to use magic wormhole, and self-hosting is too much hassle for one-off documents.
I'm aware of dropbox etc but if my both me and my mom don't already use them, there's friction to create an account and pay.
I'm not sure whether there's a business model for a standalone hosted version if Mozilla themselves couldn't make it work (and I presume they gave it thorough thought)