Is Luton really viable for a flight to India taking maybe 9 hours, and a not-particularly-long runway ? And yes, with all the extra luggage (and weight) that flights between the UK and India seems to attract. Would you put business class pax through Luton, particularly if your flight is a mix of economy and premium class pax ? It's not the same as an business-class-only aircraft with just 100 seats all of whom are paying a premium fare. Since Tata took over, they will want to get rid of the cr*ppy perception that Air India has sometimes had in the past
If Air India is to open a base other than LHR... then LGW, STN, or growing BHX seem to me the strongest contenders.
Note - before this degenerates into a Luton v Stansted war and I'm accused of being anti-Luton.... I flew through Luton over 20 times in 2022