Well you couldn't just add ice lance damage to icicles as it would add more burst in pvp.
My suggestion would be to give deep freeze a second purpose so that it can be used any time without triggering its cd to launch icicles. However if you had a FoF proc it would act as it currently does, launch icicles and trigger its cd. This prevents you from launching all the big icicles from a deep freeze combo just after the target becomes un-frozen.
I think blizz would say its too complicated but its a fairly minor thing that would allow for good players to get more out of the spec in pve and pvp.
I'm not the first person to suggest this but I think my version is a bit different.