Ease of construction and business - Like I said above, since this is an experimental line, the optimum route should have very easy terrain. Pretty much, only three routes (with important cities on them) satisfy these conditions.
The BCT-ADI route, the Delhi-CNB/ALD route and the east coast route from MAS to HWH. The MAS-HWH route is too long to be a viable experimental line, and that leaves us with the BCT-ADI route and the Delhi-CNB route.
Now the clientele for the Bullet train would be the business class, which would normally prefer...
more... flight journeys. And this kind of clientele is more abundant on the BCT-ADI sector with a considerable amount of business class traffic.
So, as an experimental line, for a proof-of-concept and also in terms of potential revenue, BCT-ADI would be the best option for a long distance bullet train experiment.