This doesn't seem to make a lot of sense as the change in Mastery (at least what I was led to believe) was to tune down burst and equalize PvP. The whole idea of Frozen Orb on a bunch of adds (i.e. Lei Shen's ball lightning adds) so you can Ice Lance spam is burst damage.
Whereas the premise of the Icicle Mastery seems to be (as other posters have commented) an ignite-like additional damage except that it's now centered on what you're targeting instead of on the target as a DoT provided you build up the first 5 icicles. The alpha (or purge) launch via Ice Lance could be a source of "burst" damage but as it is on the PTR, the individual launch speed prevents this.
Despite this flaw, this does make for an interesting mechanic of seeing just how many icicles you can "chain" together in 1 cast of Ice Lance. Especially if the icicles are not affected by Haste but FB and FBB are.
Come to think of it, that might be an interesting competition to have, a whole bunch of frost mages seeing how many icicles they can chain.