I don't agree with that, seeker. IMO, doors don't close at year 9 because a young person chooses BTECs rather than GCSEs: doors close because they get turned off education, and disengage. The most important thing - and the challenge - is to help them find something they want to do - whatever that is. Motivation is the key.
At GCSE level, they need 5 passes grade A*-C to get onto A level or BTEC level 3 courses. That's all. They don't need the 10-11 GCSEs schools put them through, and if they go on to do well on their level 3 courses, no-one will ever ask about their GCSEs ever again, except to check they have English and maths.
I know several bright kids who have taken the BTEC route, and gone on to university.
I taught on an 'access to HE course', designed for adults who had left school with few/no qualifications, but who had now become motivated to go to uni. When they left school, they thought doors were shut to them... But it's literally never too late to push on a door, and discover you can actually open it if you want to.
BTECs seem much better at motivating some kids, probably because of their practical nature. (Oh and btw, 'coursework' doesn't mean 'homework': most BTEC coursework is done in class). My own DS1 hated GCSEs and did the bare minimum (or less), and was talking about spending his life on the dole... Now he's on a BTEC media course, really enjoying it, and is talking about uni...
lljkk, my advice (FWIW) would be to help your DS find something he loves, or at least likes, that will keep him engaged. Don't worry about what he 'should' be doing: think about his motivation, because if there's something - anything - he wants to do, he'll be alright in the end. :)