cst falling of the cliff, page-23

I am not sure there will be huge sales in the "poorer countries" as you call them.
Yes, the cost of testing is a big issue (do you want to eat for the next week or do you want to know if you have a TB infection?)
You also have to determine how useful a test for TB infection would be. In many poorer countries (much of India and Africa) the rates of infection are estimated to be over 50%. I cannot see any country running tests that will be positve this often as they would then have to treat all of those that are positive (only test if you are going to treat). Any such country must firstly control active disease properly. Once this has been done they can start to think about latent infection - this will take decades.
One way to overcome this problem would be to adapt the test so that it only identified the 10% who will convert from LTBI to active disease. People are looking for such markers but none have so far been identified.