I still don't see why this would need to piggyback on a breaking change of the metadata file format. "Please use UDP by default" is fairly orthogonal to the metadata format and could be added to the spec at any point if we want to.
HTTP trackers are considered fine for medium-scale torrent deployments. UDP trackers were originally introduced to cope with the traffic caused by running an open tracker that manages 100k+ infohashes for the whole world.
Also, both BEP3 and 52 already forward-reference the tracker extensions (compact and UDP), so someone who writes a new bittorrent implementation should already be aware of them.
Maybe we could make it more clear that some BEPs are almost-mandatory.
HTTP trackers are considered fine for medium-scale torrent deployments. UDP trackers were originally introduced to cope with the traffic caused by running an open tracker that manages 100k+ infohashes for the whole world.
Also, both BEP3 and 52 already forward-reference the tracker extensions (compact and UDP), so someone who writes a new bittorrent implementation should already be aware of them.
Maybe we could make it more clear that some BEPs are almost-mandatory.