Here the main problem is infrastructure. The tracks and platforms are very limited. The same tracks and platforms are to be used for these rail buses also. It will create problem for moment of other long route trains and goods trains. Railways hardly make money in passenger trains. Their main source of income is from goods transportation. Creating separate infrastructure is not advisable.
Another point of concern here is occupancy rate will be very less. From Kakinada to Kotipalli, in East Godavari District of Andhra Pradesh., there is a single coach train. They call it as rail bus in that region. Passengers are almost not there for this train. They prefer bus. The reason they tell is bus will be stopped in many places in the village or town. So people will get down near to their house and go on foot to their house. But in case of train it is not possible. I travelled in that train one time.