It would still be annoying. Chat messages are simple and more controlled, not to mention it's just overall better. And anywho, you'll have to mute a bunch of people at one point. If someone's just blaring music in the background, mute 'em? Then mute someone when their mother tells them to clean their room repeatedly? And ban the spammer, and ban the guy making a gratuitous excess of cusses? And how are we to censor it for the soccer-moms who are afraid their little darling child hearing someone say something inappropriate? Will their be a mic sent to you when you buy Blockland, will those who have it already have to drive to Badspot's house to get them? Will their be a Blockland approved mic, or just everyone buying their own? What happens when there are twenty or more players, all trying to get heard by screaming? Then there's the problem of team chat for deathmatches and voice commands and whatnot.
There's a stuffload of problems, and a stuffload of work. It's not as simple or enjoyable as it might sound. Teamspeak is fine, but that's where it should end.