I’d say that those grades mean an applicant can be a realistic applicant. They would be looked at and those GCSEs wouldn’t work against them in terms of preventing them getting to the next stages IF their predicted ALevels are strong enough, they also perform well in admissions tests and any other criteria (such as submitted written work). Then there is the interview.
Who actually gets an offer will be determined by a mix of things, but particularly admissions tests and interviews. I’d see GCSEs and A Level predictions as a first level of application. They’ve got to be good enough to help you stay in the game. Your admissions test will need to meet a threshold to still be in the game and get to interview. Large numbers of excellent students who have perfect GCSE grades and predicted A Level results don’t make it to interview as they fall at the admissions test stage. Lots of others get an interview but don’t get an offer. There are simply too many good candidates.
Ive often heard people be cross that their relative with all 9s at GCSE and top A Level results didn’t get an offer or even an interview. They say ‘what did they want? What more could they have done? It must be prejucidce’. What they don’t realise is the admissions process uses much more than just these exams and that far more people have brilliant grades than there are places, but also that admissions tests, interviews etc test things beyond what the standard exams test.
It’s why students with good but not stellar GCSEs sometimes get in - they excel in the admissions tests and interviews and show something some of those with better exam results didn’t show. But it should be pointed out that most successful candidates do also have very very strong GCSEs. There is a correlation between the strongest GCSEs, particularly the strongest admissions tests and strongest interview scores and getting an offer. It’s not surprising really.
So, that DC in the OP could have a go. Some schools would encourage it and others would say he wouldn’t be strong enough. What he will need to do is to have really excellent predicted grades and also then to have done the wider engagement with the subject to broaden and deepen his knowledge and develop his interest and also be able to perform really well in the admissions tests and interviews, if he gets that far. When your GCSEs are not absolutely top notch, you probably have to outperform some of those whose GCSEs were better in the admissions tests and interviews. Different subjects weight different elements differently in deciding who gets offers. Loads of excellent candidates don’t get offers. But if you don’t apply you definitley won’t. So it’s worth him trying if he’s still interested at the end of yr12 and has strong predictions and has really engaged with the subject. But everyone needs to know it’s a long shot and the fact they’ve got great exam results doesn’t guarantee anything. There are no guarantees.