playing in India for the first time in the current GW#1 I also noticed the huge amount of missing airports and the very low demand.
The game year is around 1970 so of course it may be even too high compared to the real demand at that time but when I check demand in GW #3 which is in 2016 currently then the demand is far too low - so demand simulation may need to take a steeper curve than in other countries.
One of the (many) missing airports is:
Pune (VAPO) - many flights per hour to BOM, DEL, BGL, etc -
https://en.wikipedia.org/wiki/Pune_Airport but there are also
Rajkot (VARK) - today at least 6 flights to BOM by 737/A320, one to DEL by ATR
Jamnagar (VAJM) - today at least 1 flight to BOM by 737/A320
Diu (VA1P) - today at least 1 flight to BOM by ATR
Dharamsala (VIGG) - today at least 6 flights to DEL by ATR/DH8
Jammu (VIJU) - today at least 4 flights to DEL, 1 to SXR, 1 to IXL
Dehradun (VIDN) - today at least 26 flights to DEL, some to BOM, one to LKO
Allahabad (VIAL) - today at least 2 flights to DEL, one to BOM
Ranchi (VERC) - today at least 5 flights to DEL, 6 to PAT, 1 to CCU
Bhopal (VABP) - today at least 4 flights to BOM, 6 to DEL, 1 to JLR, 1 to RPR
Surat (VASU) - today at least 3 flights to BOM, 1 to DEL
i've only covered northern india and only very roughly... In the south there's
Belgaum (VABM)
Hubli (VOHB)
Madurai (VOMD)
Rajahmundry (VORY)
Jabalpur (VAJB)
Also there's a law in India that every state has one international airport. So there may be big domestic airports in some states that have no international traffic at all.
It would be really great to make India a more attractive country to play! Especially missing an airport like Pune but having a game with little airports noone knows and where you can't schedule any reasonable flights to in countries like Switzerland is a severe asymmetry in the game.
I am happy to help by assembling all necessary data so please contact me when you upgrade!