all are control their STB by viewing card (external or internal),so if all stb accept all viewing card,it will be possible.
or
centralized control system will be created by one head (TRAI) and distributed via dth operators.
but this is not possible because DTH not sharing any between them,they have their own rental satellite and separate encryption methods.so the future plan it should be "a card )like sim card) should support all format dth streams build-in security access key."