Eh.
I am really not sure about this one.
The main problem would probably be simply that the definition of what is mic-"spam" is different from person to person. One might consider a certain song mic spam, while others consider it absolutely amazing.
Or people yelling into their mics, but still contributing to the game - for example people that tend to yell when they get shot at, which some people could take as mic spam.
Or, one of the most important topics, little kids using their mics. Many consider that as extremely annoying and would LOVE to get them muted - inb4cyberbullying.
Some mic spam is annoying, I agree - mostly the ones with terrible quality.
The thing is - sure, you say now you can report, but what happens when someone reports someone for a wrong votekick? "Dude, it's a kick."
Why are you sure that people (and admins) won't just say "dude, it's just a mute, don't use your mic/mic spam for five minutes".
All in all, I doubt this function would bring more than people complaining about it.
Pressing ESC, then playerlist, then mute in-game voice is still faster than typing votemute, selecting the name and naming a reason.
tl;dr: not sure if want.
EDIT:
And what about people that just keep mic spamming after getting muted?
I'm sorry, but I just don't see any use in this.