There are notams covering the use of CPDLC in India, discussing who can use the service.
There are many many places using it... Yangon (amazingly), China, Ujung, India (Kolkata and Chennai have had it for a long time... Delhi has just started) and obviously Australia, Oakland, Auckland, and Maastricht.
In Maastricht, it seems to be used to monitor flights, and occasionally give direct routing clearances. It used to be that a level change instruction given by CPDLC then required a voice readback.
In Maastricht it is a supplemental service, it isn't the primary mode of communication. You are still always on a voice VHF frequency for immediate contactablity if required.
That isn't the case when its used as the primary communication method, for example over the Pacific ocean AUS - US. Lower separation standards are allowed for two aircraft both on ADS.
At the moment it appears India are just using it as a monitoring tool, and a comms method, and not to reduce separation.
We use it all the time, but then, my company tells us to!