Chiranjeevi is from Telugu Film Industry na. Nobody stopped Mammotty when he was awarded the title of Megastar.
It's each individual's achievement. Srk already is referred to as King / Baadshah of Bollywood while Big B is called Shahenshah of Bollywood / Star of the Millenium too. Why shouldn't Salman get his own title especially the one he is worth of + earned honestly.
Akki on the other hand can be called a superstar but not a megastar.
And we all know once you use the term Superstar it's by default Rajinikanth but that hasn't stopped others being called the right? Mahesh Babu got superstar tag from his father Krishna whose title was superstar. Bollywood star titles don't work like it does for South heroes. Just the fact.