Dream role for Sangster
This young actor seems to be very interested in aeroplanes and flying, especially the older ones. The timeline 1920s to 40s is what he's focused at. It's mostly about war times, and he's expressed the wish to play a pilot fighting for Britain.
Sangster has the right age to play someone in the army. Why not cast him in such a role? Buy the kid a pilot jacket, goggles and stuff, and there you go.
I just came to think of a certain english flyer who joined the forces already at the age of 17, and fought in WWI. It was an older boy with slightly red hair, brittish manner and "woman hands", I have heard. Does this sound like Thomas Sangster? He does look younger than his age and is a feminine boy, so it could work out very well. And I don't write this to be mean. I really want him to play something cool.
If the studios don't believe him to be a public magnet enough to play a lead in a movie, then make a television production instead.