If we're going to make such a big deal about movement, then it should probably be pointed out that if the movement is going to take long enough, you're going to be topped off before you reach the boss. Thus, not getting Shuffle up immediately won't kill you.
Nevertheless:
Moderate "worst-case" scenario (no KS, but you do have the energy since you ran around):
Average time for Shuffle (hard-capped): 2.00 GCDs
15% negation (7.5% failure): 2.16 GCDs
7.5% negation (15% failure): 2.35 GCDs
0% negation (22.5% failure, unreasonably attainable): 2.58 GCDs
These time frames aren't really radically far off from the hard-capped setup. While, yes, you can't have a fractional GCD, the decimal serves to illustrate the probability of having to spend an extra GCD. The closer the decimal is to 1, the more frequently it happens.
Chi is not refunded when Blackout Kick misses because Shuffle is applied. Otherwise, you'd want to miss Blackout Kick for free chi.
This would be why you front-load your threat on a taunt swap. This is not a radical idea even if you are hit/expertise capped, and the nature of the relationship between energy/chi allows you to do this with no loss.
This is by no means a compensatory measure, and as much as you all seem to hate and harp on having even a 1% chance of failure, logically, then, it would strike me odd if you didn't already do this. But you probably don't, because if you did, you wouldn't have posted this.
Shuffle hasn't been the arguing point for haste.