With the proper talents, Mind Flay would refresh Shadow Word: Pain and Drain Life would refresh Corruption. This gives more utility to channeled spells, which normally require its full duration to run for optimum effect. PvP, in particular, requires constant motion which gimps the use of channeled spells. If the proposed changes push through, this means that channeled spells can be used for a short duration in order to refresh existing debuffs. This is an incredible trend that I hope makes it into live as well as extend into other, channeled abilities.
This change should hopefully see the use of more channeled spells in PvP, with players stopping for the briefest of moments to channel a spell in order to refresh a debuff. Even direct damage spells with casting times will be used to refresh debuffs, making it useful even for PvE. This is significant in PvE DPS cycles because players will no longer need to break a spell cycle in order to accommodate re-casting a DoT, which often activates the Global Cooldown.
The direction that Blizzard is taking with the new spells -- adding more utility and new mechanics -- is an exciting one. It's a small thing that will change how some spells are utilized. I'm willing to bet that in the future, we'll be seeing more flashes of channeled spells bolting through in the Battlegrounds and Arenas. Given that the talents outlined are but a sampler of what will be in Wrath of the Lich King, I'm hopeful that we'll see more of this mechanic across the board. When more Alpha information comes out, it's quite possible that we'll see a Hunter talent that refreshes Stings, or a Rogue ability that refreshes Poisons. From what I see now, WotLK looks very promising for channeled spells and abilities. I can only hope they make it to live!