Whats next Botnet Command and Control?

We have seen plenty of ways to do Botnet command and control in the past and it has evolved since then, so whats next and latest ways we are seeing for C&C, and how can we fight those ways.
Can gmail, yahoomail or any other mails services can be used for command and control, if yes then it could be the next generation of botnet command and control. And I believe it can be very much possible in comming days.

Can someone have some good thoughts on this?