Having checked luggage seems to be the factor that requires travellers to get visas because they have to collect their luggage and check it with their airline
This is simply not true. Immigration and customs go hand in hand -- they won't build an entire "sterile" transit section and put relevant rules in effect for the few people who don't have luggage. If you'd need a transit visa with checked luggage you need one without one as well.
With that said, http://www.cgitoronto.ca/content/faq-about-visa-0
I will be changing flights/airports in India to travel to my final destination (say Nepal, Thailand etc.) Do I need a visa to change flights/airport terminals?
You need to apply for a transit visa if you are going to change from an international terminal to a domestic terminal of any Indian airport or if you are going to stay in an airport hotel even for a few hours. You don't need a transit visa if you stay in the waiting area reserved for international transit passengers in an Indian airport.
You might not need a visa at all. But luggage is not a factor.