I really really really don't like this at all. The problem is that you are forcing malzahar to farm in between every use of his ultimate. This has several negative implications.
The first is that a Malazahar that is behind will never ever get to reach a decent amount of damage because he will never have access to the farm he needs to "charge it."
Second, you punish multiple uses of the ultimate in a short period of time; if I try to pick off a single target and succeed, and they my team goes to do baron and then we back, my ultimate is off cool down but, seeing as we are probably about to enter another period of teamfighting, have no time to restack my ultimate. Essentially this is a VERY heavy nerf in the late game where there is less emphasis on farming and teamfighting becomes more important.
Third, you are talking away some of the only CC that Malzahar has access to to stop melee champions from running him down freely.
Lastly, it becomes VERY difficult to figure out how much damage your ultimate is going to do because of the sheer number of combinations of stacks one is capable of achieving. In addition, I just noticed that there would be a massive problem since his voidlings scale off bonus AD and do physical damage, so this would actually be a massive nerf to AP malzahar's damage.
Basically, as a low CC champion (outside of his ultimate he has only a silence, granted a long silence but still), Malzahar would suffer greatly without his ultimate. I think people just need to learn how to play around the ability. Its longer than the range of his other abilities, which means, as long as you stand back, he should never be able to put more than just his ultimate (and possibly ignite, not sure about that one) on you at once. What I mean there is that if you are getting hit by E, Q, and R'd while standing on the W, you screwed up. Bad. In addition, Malzahar CC's himself and any hard cc'd interrupt his ultimate. So while his ultimate is dangerous in a 1v1 situation, in teamfights its much harder to use effectively.
