A buff for Heimerdinger

Hi everyone.

When playing Heimerdinger, if you use any ability, and then try to ult afterwards, you need to wait for the cooldown of your abilities first. You can't chain grenades or rockets.

EG) Use regular grenade > Try to ult > You have to wait x seconds for regular CD to come off before using upgraded grenades

I'm hoping for Heimer's ult to behave like Rengar's fury system. Rengar (IIRC) can chain abilities even with the regular cooldown, and after using his hyped ability, the regular cooldown still persists. I'm thinking of something like this:

Use regular grenade > ult > Use upgraded grenade > the CD of the regular skill still persists.

If you think this is a bad idea, I'd like to know why you think so. Thanks for reading.