well as stated above, Vitz/Yaris has a well established market.
CNG is not a wise option for CVT automatic transmission. But in manual trans you can install CNG, no problemo. However, majority of vitz cars (in fact all JDMs cars) i have noticed that they are being run without CNG. Particularly if petrol average is good then no need to burden your car and pocket with a CNG kit.
For commercial use, Toyota Hiace is much better. good for CNG, parts availability, service and of course good resale.