MIG-31 is an engineering marble but it is not fit for India's requirement ( except reconnaissance ) because of few reasons.
1. MIG-31 is a plain interceptor as Russian has to defend vast territory and need to reach faster toward enemy as Russian bases are situated much inside the border or large gape between the air bases.
2. MIG-31 is not a dog fighter ( MiG-29 is designated dog fighter ) it's job is to reach early and scar enemy by firing long range AAM.
3. Earlier MIG-31 fly half of its flight like a passanger plane due to high fuel load. No maneuvering at all, not even sharp turn. There was a crash when fuel indicator malfunctioned and pilot turned jet.
3. MIG-31 is good in escape from enemy fire but bad in dog fights. Nonetheless, MiG-31 good in ambush attack.
4. MIG-31 is very costly in maintenance. Pilots use space suite, MiG-31 built by literally welding it's metal sheet, means no drilling or rivets.
5. Zero Air to ground capabilities