> On the sender side, the "send via" option can appear in the standard sharing app list.
Can, but does it? Defaults matter. And how would the receiver be notified that they should download some file via FTP?
As long as such a feature does not come preinstalled on smartphones, I'll continue considering this lack of previously commonplace functionality an intentional vendor lock-in.
>how would the receiver be notified that they should download some file via FTP
You tell them "hey I want to share a file with you, scan this QR code". The QR code sets up the WiFi Direct connection, the fake portal login should auto-open a "click here to download" button (or redirect to a file, but I don't think that's allowed), and once the file is downloaded you terminate the Wi-Fi Direct connection.
But that presumes phones don't have a method to share files. They have that feature built in. It's called Nearby Share on Android and AirDrop on iOS. Both use some weird pairing mechanism and some form of Wi-Fi Direct to transfer files, but the interface is just a bit more integrated.
When Apple opens up Airdrop or when Google convinces Apple to pre-install Nearby Share, we'll get the universal file transfer we desperately need.
Can, but does it? Defaults matter. And how would the receiver be notified that they should download some file via FTP?
As long as such a feature does not come preinstalled on smartphones, I'll continue considering this lack of previously commonplace functionality an intentional vendor lock-in.