I think there are some ethical issues with trying to find those people and not treat their disease before it is too late, most of the testing will consists of preventing people from becoming good test subjects.

I'm not saying it's bad, but it will be expensive and may fail to yield much result (as far as testing the cure goes).

Treating them is the point. Find people who's too late to get the old rabies shot and give the new treatment to them. The difficult part is control group but that's always the difficult part. Without control group they can probably just compare statistics with the past...

I don't think you really need a control group for something with a well established nigh 100% fatality rate.

The fact that 20K people die to a disease that has a set of proven, relatively inexpensive treatments tells me that 20K people already can't get to a medical facility.

Getting to those people to a medical facility to test a new, unproven, expensive treatment simply isn't going to happen.

This is especially so since there are a vast number of diseases that are much higher priority than rabies in India.

I have unfortunately seen some heartbreaking videos where it's children who got it. Some for sure can't get access to medical care in the rural areas, but sometimes the kids might not even know.