Interesting that the people on this board seem convinced that we are definitely moving to post qualification admission - and seem confident that the OP's DS will be caught up in that as a current Year 7.
As I understand it, the government has just called for consultation not made a definite decision (when is the consultation, which I gather has closed, due to report, or has it done it yet? - can't find anything on google to suggest they have reported). There were some surprising nay sayers eg:
www.teachfirst.org.uk/blog/post-qualifications-admissions-system
And see some of the concerns expressed by UCAS in:
wonkhe.com/blogs/ucas-cautiously-recommends-a-move-to-post-qualification-offers/
Noting particularly :
"It is likely that the impact of the Covid-19 pandemic will continue for some years to come. Negating the effects of the pandemic will be the priority for all of us in the education sector, so there is no doubt that we should plan our next steps very carefully. As we emerge from two years of no exams and disrupted learning, we are strongly recommending a full consideration of the timing of any reform implementation.
It is vital that any significant change to the overall model is confirmed far enough in advance so that applicants and teachers know the rules of the game and students can be adequately supported to navigate the changes."
There are a lot of people who would not be keen on more upheaval for the next few years at least. And then there is the question as to how it will work with those courses that require interview - as the model advocated by UCAS leaves no time for interview (and probably not chance to apply to do something else if you fail at interview). I grew up and went to university in a country where all offers were post the receiving of high school results - you applied to the various courses in order of preference, and when your grades came out, you knew whether you made the cut-off or not (each subject gave a score out of 100, and it was your best 4 out of a hundred and ten percent of your remaining subjects, if any, and the universities just put the applicants in total score order, and went down the list until the number of places had been filled)- but there was a lot of criticism about medicine in particular, because there was no interview, just whoever got the best academic scores got in. I just can't see the medical schools here accepting that And funnily enough, on my gap year, I meat a whole bunch of British students, but they were all ones who had applied to Oxbridge, because Oxbridge had its exams and interviews post finishing A levels, so they did their exams and interviews and then the rest of the year was a gap year. And when I asked many years later why that no longer happened here, I was told that it was considered to be unfair to disadvantaged students, who couldn't afford to take a gap year (or were too scared to risk it), so they stopped it as it was keeping Oxbridge as a bastion of privilege.
So it seems to me that there a huge amount to iron out for post qualification admissions to work for medicine/Oxbridge. And even if we grant that the medical schools will somehow manage to run around and have all their interviews in late August/early September (when most of their staff are no doubt on holiday), they will still need criteria over and above the A levels to determine who to interview, if A levels stay as simple grades, and not a scoring out of 100 so you can finely differentiate - the alternative being that it is not just the admission process, but how A levels are reported that would need to change. And each medical school will still choose to make that decision in different ways, and Year 13 students putting in applications (because the most popular model still has them applying while at school), will still have to apply strategically to get that interview. And the tips for medical interviews won't change, and the need to review how each university scores post interview won't change. Which means, it seems to me, that the system has to be more familiar than different. The only real difference will be that instead of using predicated grades as one of the many filters, they will use actual grades. And the timetable will be shifted. Can't see how it will work any other way.
The really big change would be if they insisted on postgraduate medical courses only, with the medical schools no longer taking school leavers, as some other countries do. Now that would be a huge change, but I don't see that one by the time the OP's DS is applying.