People I believe I have figured out SM cycle, as we all know exo debuted when shinee was promoting Sherlock so he in what I think from seeing this cycle :
Mr, simple-suju
The boys-snsd
Sherlock-shinee
Mama-exo
Electric shock-f(x)
Catch me , humanoids-tvxq

Then the cycle starts again

Sfs, spy-suju
I got a boy-snsd
Dream girl-shinee

So if my calculations are correct exo should be coming back, during it after dream girl promotion. Lets have our fingers crossed