DS1 started in 6th form last month, and was dithering between a school with an expanded 6th form which markets quite heavily to recruit external students, and a standalone 6th form college - he'd applied to and had offers for 5 places (in total!) to do Maths, FM, Physics and Philosophy.
Not sure about the other 3 but the two he was torn between both do Maths this year and FM next year. Apparently most students in his 6th form start with 4 A levels and they can drop one at the end of year 12, but parents have had an email saying that they expect students in Maths and FM to stick with the 4.
I think both require 7 for Maths and an 8 for FM, and that seemed to be normal for the other places he'd applied to. The college wants an average of 7.5 in the 8 best GCSEs to do 4 A levels, though quite a lot of their students (other than those doing FM) do 3 A levels anyway, and generally results are quite good.
I can see the potential logistic problems that you mention though, @noblegiraffe.
We have a tutor review meeting online this week, though I'm wondering what it means that they've cut the meetings from 14 minutes to 9 - I understand they've taken in more 6th form students for some time but did they suddenly expand a lot this year?