Satellite or radio based ISPs, mobile networking, and if we get exotic, interplanetary communications all come to mind as environments which fit all three criteria.
Also, this scheme is not really asking for massively over provisioned lines; we're looking at fairly small data sets with infrequent bursts to larger sets, and an ack from the receiver knocks the size back down again.
That said, if I were implementing this, I would probably implement a sliding window for messages I send (waterfall encoding would work great here, though it is patent encumbered), and add the ability for the client to request a set of messages it missed. This would make the traffic a bit more predictable and offer the server & client the ability to make up for traffic which was lost during its send window.