Idea for Kassadin changes

I know that Kassadin is in a fairly healthy state right now, but one of the frustrations that many Kass players experience is the lack of a way to avoid/mitigate damage in teamfights. Other assassins such as Ekko, Zed, and Fizz all have untargetability options which allow them to not get blown up instantly if they try to assassinate a target who's protected by allies. Kassadin has his insane 2 second CD ult, but that's often not enough to feel useful in teamfights unless you have Zhonyas active ready.

What if Kassadin gained a brief invulnerability (~1 second) if he casts Null Sphere (Q) when Force Pulse (E) is available? In exchange, his ult CD would be higher at later ranks.