Insat 4A will continue little longer and C Band chs will remain there till then, also with Ku band becoming free load will be lowered thus increasing life of satellite.
2ndly GSat 10 was supposed to be additional satellite to Insat 4A for Tata Sky but as its launch got very delayed hence ISRO offered it to TS as replacement which they declined to accept. Hence to accomodate needs of Tata Sky and provide future safety net , C Band on GSat 10 was kept empty so that life of satellite can be increased. Later on C Band chs of Insat 4A will move to GSat 10
Govt. had tried to bring in policy for making indian broadcasters shift to local satellites but it was not feasible. There were issues of not having adequate teleport infrastructure , coverage area being limited as well as other issues which i don't clearly remember