syed, the Indus Motors has announced to produce only Xli in CNG version.
tiptop your friend is surely one lucky hell of a guy but how can you say the same is going to happen with the others? Waisay the only other cars that have the same are Civic Vti Prosmatec, because they have to get rid of the old shape and Altis because they've already been produced and no one's willing to buy them.
khandada, i now see that you're somewhat right. RXi is available in both, CNG and non CNG versions. The CNG version is available in 4-5 months whereas the normal one is either readily available and if not, is delivered within one month. In case you're one of those kind who always want the latest year, i'd suggest you to book yours in the last week of December.
As for installation of CNG later, there are some reservations. I do not know why but installation later is not as good as factory fitted. I myself have driven a later fitted Liana in particular and found it not to be so good. This is the main hunch of there being chances of not getting a good price for this car in particular. Otherwise it's a known fact that installation of gas increases the price of the car by nearly Rs. 50000.