This wouldn't work because it ruins what makes Malzahar difficult. Positioning. He needs to have great positioning in order to do well later. Having voidlings channel his ult would be far to complex and difficult. Now, something I wouldn't be against would be Malzahars voidlings gaining passive bonuses from his ult when it's leveled up. Such as more attack damage, or it shreads armor and magic resist each hit, or something. This would be an amazing buff for Malzahar.
Also, a few fun facts about Malzahar...
His voidlings scale off his AD (1:1 scaling off AD)
Voidlings apply on hit effects such as Wits End, Black Cleaver, Frozen Heart, etc, etc.
Voidlings scale off Malzahars armor pen.
Malzahar can play EVERY lane and role, be it mid to jungle. ADC to Solo Top.
Syndra can throw his voidlings.
With 40% CDR Malzahar can have two voidlings up at all times.
( Still Testing, probably false ) Malzahars voidlings trigger spell vamp