@*hughs, I'm not sure which A-level doors are being closed off by 8 GCSES - often fewer than you think.
DD2 has just picked her sixth form options - I think Art was closed to her (she hates art though!) but that was about it. Languages she would have had to take a test before taking the A-Level. Music would have needed theory and practical certificates.*
I guess it depends what's compulsory and how many options they have. At my DC's school there 9 were compulsory, so that obviously would reduce choice somewhat. There you couldn't do history or geography A level without GCSE. You couldn't do maths (or physics I think) without additional maths. A language test is fine, but if you can't do the GCSE at school, how will you have gained the necessary skills? Would A level only be available to those who speak the language at home or can afford out of school tuition.. Same with music, GCSE is the pathway to A level for kids who may not be in formal music education and taking grade exams.
I don't think it's controversial or really even debatable to say that making kids choose 8 GCSEs is more restrictive than letting them choose 9, 10, 11 or more, and that many don't know at 13 what they want to focus on.
DD was a classic one of those who enjoyed a lot of subjects. She was lucky to be allowed to do maths, English, Welsh, history, RE, triple science, drama, French, add maths and economics. (And Welsh Bacc.) She enjoyed most of her courses and went on to do four A levels because she still had a wide range of interests, and is now on a major/minor interdisciplinary type degree course with a compulsory language and year abroad. I'm sure 8 suits some, those who pick a lane early and know what they want to do, but for kids like DD, 8 GCSEs is a terrible shame I think.