Engines are not a problem, all these are substitutes till kaveri arrives, And Yes there would be structural changes, No, not after 40 aircrafts, Airforce has so far ordered on 40, And would order more, But Airforce is Interested in LCA mark 2 version which is exactly built as the needs of IAF, Now a question arises, Is LCA mark 1 not asper the needs of IAF, the answer is,Not fully, the design concept is old and was suitable for a 4th gen aircraft and The role of LCA mark 2 would be entirely different for LCA mark 2....
Without getting the money invested how can you continue the research?? Now that we know how make a 4th gen aircraft, it would be a lot more easy for Us to make LCA mark 2, it makes a lot of sense if you think positive