I always use to say to my friend who mains Talon that the silence is what made Talon OP, im glad they are removing it but i dont really like what they are replacing it with. As for Viktor i thought his silence was alright, it was very short and it didn't seem stop most abilities anyways. Interrupting channels is a good replacement at least.
Removing the silence from Malzahar would make him even more useless then he already is... His silence has tons of counterplay, its called dodging. It has a delay before it hits and it broadcasts it pretty obviously. He needs the silence to set up his W - R combo otherwise they will just flash or dash out before you can ult or you will still ult and do no damage.
On Garen i think the silence should be a slow instead, it would mesh well with his E. But im pretty sure removing the silence on Garen would make him useless against certain champs and he would stop countering a lot of tough tops.
Cho'gath and Blitz silence need to be changed, there is no skill or counterplay involved.