While they seem to be unsure about the issue, a developer recently said that hasted channels may or may not work the way hasted DoTs will. That is, they may add extra ticks to channeled spells to leave the duration of the channel unaltered by the haste. This is far more bizarre than their plans for hasted DoTs.
While there are some important differences in the game between a channeled spell and an ordinary spell that resolves at the end of its cast time, they interact with haste in exactly the same way. Fireball takes three seconds to cast, Mind Flay takes three seconds to cast. Put 100% haste on them and Fireball takes 1.5 seconds, Mind Flay takes 1.5 seconds. You cast more spells when you have more haste.
Unlike DoTs, making channeled spells interact with haste in this way would not increase dps at all. You would spend just as much time channeling Mind Flay either way, and do the same amount of damage in that time. What it would do is increase the mana efficiency of channeled spells. Why would they want haste to increase the mana efficiencies of channeled spells and not of direct nukes?
Of course it would also do some other crazy things. If you had haste procs that affected a certain number of spells (imagine a Nevermelting Ice Crystal for haste instead of crit) then it would mean that extra haste would become more effective at increasing the damage of your channels than increasing the damage of your nukes. The equivalence of damage and nukes relies on the haste being the same for both. If you can do a big haste for one spell, it is more effective on a channel. This is because 100% haste on Mind Flay means casting Mind Flay at double speed for 3 seconds, while 100% haste on Fireball means casting Fireball for double speed for 1.5 seconds. Basically, if you only get to cast a certain number of hasted spells (as opposed to casting hasted spells for a certain amount of time, in which case it makes no difference) then you effectively get to increase the number of hasted spells by the amount of haste granted if you cast channeled spells instead of non-channeled ones.
This is totally unintuitive (haste doesn't make things faster, it makes them do more damage), makes bizarre distinctions meaningful (haste has a significantly different interaction with channels compared to direct nukes when applied to a number of casts but is essentially the same when applied over a duration), and in the end changes almost nothing about how we actually play the game except in strange edge cases. Going forward with this plan would be ridiculous.