Sorry for bumping up a really old thread. I travel very frequently with Indigo and since a few months, have started seeing fqt2 in the special services. I was not able to find any information on this until last week when I was asked for weighing of cabin baggage. I generally carry a strolley along with laptop bag. The strolley was weighed and found to be 7 kg while the laptop bag was around 3kg. That's when my boarding pass was checked and I was told that I am frequent flyer and hence am entitled to 10 kg cabin baggage!!
I am still looking for someone to further enlighten me on this.