One of the standard and frequent arguments given out by Railways against starting any new service is "Congestion". However, the figures of Occupancy (or Congestion) given out by Railways are a very positive set as far as Blore City-Yesvantpur(YPR)-Yelahanka(YNK) Airport Train is concerned:

(1) KSR Bengaluru-YPR - Capacity utilised - 63%
(2) YPR-Yelahanka (YNK) - Capacity utlised - 50%
(3) YNK-CBP (via Airport) - Capacity utilised - 29% 
Speaking about the possibility of introducing trains to the airport, a railway official said though the line was clear, congestion at YPR station makes it difficult to run trains. "The morning and evening hours see peak occupancy in stations due to the arrival/departure of long-distance trains," he said (see  -  https://www.deccanherald.com/city/delay-suburban-rail-spv-hits-694218.html ). However, since the peak (maximum congestion) timings for Railways is limited to a few hours, and the Airport works round the clock, the problem is not insurmountable. Indian Railways has the required expertise to handle this very easily (e.g., Mumbai)

The above figures show a clear possibility of quickly starting the Airport Train from City via YPR and Yelahanka to the Airport. In fact, with implementation of AUTOMATIC SIGNALLING, the congestion factor can be brought down further. Only the WILL is required. Problems and challenges can be solved. A small, single-platform Airport Railway Station to begin with near the Trumpet Interchange, suitable parking area and 2 ramps to connect to the existing internal Airport Road, 2 low-floor EMU Trains, 4 Buses, and some technical expertise are the ONLY MISSING LINKS. Once this service starts, plenty of add-ons can be implemented. We look forward to AIRPORT EXPRESS from City to Malleswaram to YPR to YNK to AIRPORT to complete the trip in 40 minutes (total distance 45kms), including stoppages. So, Railways must start work on the basic Airport Station and everything will soon fall in place.