To be honest, I think that the market (both print and e-book) is saturated; every man and his dog has jumped on the BIR book-wagon, and there is so much useful stuff available online (both here and elsewhere) that there is very little incentive for the would-be-BIR-chef-at-home to buy something when the same or better information is available for free. These days the only Indian cookery books I would even /consider/ buying are those written by authors from the sub-continent -- I believe that we can potentially learn a very great deal from those who have Indian food in their genes, whereas with one or two notable exceptions (Mick Crawford being one), books written by Britons tend just to trot out the same material, all of which is available online, in the guise of being new and different (which it never is).
P.S. From a purely personal perspective, I would never buy a book that offers to teach me how to make healthy food -- a book that could teach me how to make the BIR curries that I experienced in the 60s and early 70s, on the other hand, would be an absolute God-send.
** Phil.