Riot should revert Celerity to what it used to be, then do one of those changes:

1. Buff its movement speed back to 4% like it used to be in the beginning. However, remove the AD/AP conversion completely. Make this rune be only about giving movement speed, no other offensive stats. Don't know why it used to give AD/AP to begin with. Movement speed is already a great offensive stat by itself. This only served to add to the power creep.
2. If Riot really wants to keep the AD/AP conversion, at least make it so that Celerity's effects do not apply until level 10, like Transcendence. This can even allow Riot to buff Celerity's AD/AP conversion, possibly even the movement speed amount. Because this rune will be balanced by the fact that you do not get its effects until level 10, so you are essentially playing with one less rune, which can impact your early game. Transcendence works like this.

They shouldn't have reworked Celerity into this. It is a complete noob trap.