Okay, second try. Thanks Post Monster!
Is there a fatal flaw in applying the counterspell mechanic to channeling?
In other words a 5th Cleric could "counterspell" another 5th Cleric or reduce the 7th Cleric's channel to d6?
If combat was Cleric vs. Cleric and the first Cleric wanted to ready an action to counter channel the second Cleric and the DM is happy with that mechanic then I don't see why there should be any major issues with it.
It is a little clunky though, and I'm thinking that, like counter-spelling, it isn't going to happen all that often. It looks like a wasted action to me, the second Cleric could cast Finger of Death instead and the first Cleric would have lost a turn, better to delay and act after perhaps, negating whatever the other Cleric did?