Right now one is so obviously better than the other, even given the increased cost, that few people actually remember that Cloak and Dagger exists.

Xypherous hinted that Phantom Dancer would be getting a from-the-ground rework once the Season 2 finals are finished. The reasoning being that Phantom Dancer is the best choice both for top DPS and for utility for the Ranged AD class, creating a massive stagnation in build options. Unofficially, he pretty much said that the movespeed on Phantom Dancer (and likely Zeal) will be getting nuked, and probably put on an item with Tenacity, meaning Cloak and Dagger.

This is, of course, not an official statement in any way, shape, or form. It is also possible that it is/will be toyed with for some time before being thrown out due to causing more problems than it solves.

^^^ Ouch.

If that does happen, Hecarim will need to be redesigned. There are five +% move speed items. One of them, the Zeal, builds into two of the others, so there are actually only 4 finished items. Removing the move speed from Zeal, Phantom Dancer and probably / partially Trinity Force would leave only Force of Nature and Lich Bane untouched. That is not a lot for Hecarim to choose from. Sad days.

Trust me, if these changes cause problems with Hecarim, he will receive custom changes to fix him at some point. This is because Riot balances the champions very well individually, and item changes will affect how they need to be changed.

This is also why item changes are very rare. Balancing 90 or so champions is hard enough without someone messing with the items every so often, which would require several further sets of changes to every champion who is affected.

Xypherous's post indicated that the movespeed would be moving from Phantom Dancer to Cloak and Dagger, not that it would simply be removed from the game.

Also, if you're building Hecarim completely around movespeed items, you're doing it wrong.

And this is exactly why Talon and Renekton still have to wait for the AD Caster Spell Vamp ArRedux Aura item -- thus far, it's either been blatantly OP or marginally beneficial.

And the biggest obstacles to them obtaining this item are Jax and Akali, sadly. It will have to somehow be simultaneously useful to Talon and Ren AND not a massive boost for current hybrids.