[namibj]

Well, https://www.bittorrent.org/beps/bep_0014.html isn't even that new, and yeah, it's only for service discovery right now, but I'm pretty sure you'd get multicast support in the popular clients, at least for Merkle-Tree (BEP-0030) torrents with e.g. 2^10 piece size.

[the8472]

BEP14 is totally irrelevant to the discussion here. It's only for finding peers in a local lan, not for distributing payload via multicast. The latter is and always has been via unicast.