When yum downloads updates from multi repository. Now, yum downloads only one update at a time. But if yum can downloads some updates at a time, I think get yum downloding faster. Yum use not only one repository. And updates often exists not only one repository. So yum can gets file A from repository B, and at the same time gets file C from repository D. Different repository often means diferrent server. Acutually, APT ,which is a Package manager like yum, can downloads more files at a time. Why yum can only one file at a time.
Downloading multiple packages at once makes the display impossible. Patches will be considered, but it's not something that is inherently interesting to upstream development.