Boots of Swiftness are used less often than nearly every other type of boot. There are select cases and champions where it is used more often (Garen, for example), but I feel it is just not competitive with other boots.
A simple change could make them much more useful for various situations, as well as fit in with the design of the boot (to run slightly faster). I propose adding a unique passive of avoiding unit collision. This would make the boot more useful to junglers for ganking purposes, more useful in lanes to avoid being blocked by minions, etc.