Most of the existing operators having heavily invested CS Core network elements across the entire country. Launching IMS Core as a replacement for these network elements is not a easy jobs from the economical and practically not that easy.
Geography & Customer base are huge with highly complex interconnects across the nation.
SRVCC requires top quality GERAN/UTRAN .
Which is still a question mark....due to many factors including the above pointed Geo + Population.
Even-though Reliance JIO starting with LTE + IMS Core , it may not have a strong target GERAN/UTRAN network. I don't think that there is a partner to do so, instead they may opt for CSFB which helps RJIO and its partner in more better way in terms of implementation.
The 1800 MHz they have acquired is not for GERAN/UTRAN instead they may use it for LTE-FDD Network.
So conclusively, SRVCC may not come to India...
Figure 1 :- SRVCC Concept Diagram from Radisys Whitepaper
SRVCC Background :-
With IMS as core (already deployed), SRVCC become the ultimate choice for Japanese and US mobile operators to provide multimedia services. It was easy for them to go for SRVCC instead of troublesome CSFB ( only in congested areas) with complicated requirements in terms of tecchnical capabilities at UE & Network.
Figure 2 :- SRVCC ecosystem
Figure 3 :- SRVCC Evolution Path
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