I must admit, my son is cheating so slightly, he's doing A level French and he's a French speaker, it was hard to not add it on but wasn't on his original 4AS/3A2 choices, it's purely for UCAS points so he's less stressed with achieving in his real A levels. I tried to get the school to drop the GS but didn't win that one, so he does 5. Definitely not recommended to do 5 A levels, but it sure fills the timetable.
It's very much every country has a different take on university entry in the rest of the EU. In France and Belgium for example, if you turned up with A levels, the grades would be irrelevant except for medicine and engineering and the like, whereas next door in the Netherlands, they are more picky about who starts first year university. Each EU country has theoretically an equivalence system for those travelling across boarders and applying for university and jobs, where they register their EU qualifications and you get an "equivalence certificate". IB of course is going to be more familiar and qualification for recruiters than A levels, but again depends on how many schools in each EU country now uses IB.
For my children educated and previously educated in a country where Maths, Science, 2 national languages, religious studies, all these subjects are obligatory to age 18, plus where children do huge numbers of hours of homework if in academic streams of secondaries, IB would be easier for most than A levels, were either of these qualifications to be introduced into schools, simply down to the breadth of current curriculum and work levels. Not really the case in the UK, where children drop subjects age 14 and then age 16, A levels is a natural progression and IB is less natural for many.
I'd hope if there is the possibility of either at the same school, that the teachers could indicate the best of the 2 systems to follow age 16.
I wonder if UK universities made their offers on more than the usual 3 A level subjects only and not on total UCAS points, that more students would opt to take 4 A levels as standard rather than 3?