2. Some of it could, yeah. Torrents make it easy to share files directly from your computer to a peer's. FEX solves a slightly different problem, though—the asynchronous "put the file somewhere, then let the peer get it while your computer is offline" use-case. It's somewhat cumbersome to use torrents for this (though possible: you and the server join the swarm, the server leeches from you, you leave the swarm, the peer joins the swarm, they leech from the server.) But, if you do use torrents that way, you won't [by default] get the "auto-deletion of the server's copy" property that FEX has.
(You could probably match 99% of FEX's functionality with a torrent client running on a server + a daemon running alongside it that can control the torrent client through RPC; but I don't know of any attempt to build such a thing.)