Metalink support would enable traffic distribution, integrity check (file checksum) and nice download resume (most meta4 aware download clients track download progress and can resume download in any point). Optional fragment checksum feature would enable re-downloading only broken parts. New ?meta4 endpoint would contain data from ?mirrorlist and ?sha1/md5, could also contain file size (that currently can be obtained only from Content-Length header) so it would help allocate disk space before downloading.