sudden impact good on kassadin?

i haven't seen a lot of people use that rune with kassadin.
the main reason i heard, it's because it's a 4sec cd, and your ult maxes out at 1.5 sec cd, so basically by lvl 16 it's useless.

but i feel that pre 16 it might actually be useful, since your ult lvl 1 has a 5 sec cd, so you can proct it twice or three times in a fight. at lvl 11 your ult has like a 3-4 sec cd so it's perfect, meaning every blink you will proc it.

any thoughts???