Sharing identifier maybe we could do with qrcode, chirp audio protocol, nfc tap. Ios has peerconnectivity that works really as p2p network but sadly no web api and doesn't work android (not sure someone reverse engineered protocol)
Somebody indeed has, but since it uses a custom low-level 802.11 variant, I don't think it's feasible on (at least non-rooted) Android devices: https://github.com/seemoo-lab/opendrop
