I know it will be different elsewhere, but in my sixth form, everyone is still sitting all their AS levels. They'll be used as indication for A2. The only reason everyone is sitting is because the school can afford to waste money on ASs that don't count.
If you're dropping something, the AS can be "cashed in" so that it does actually count. But if you're continuing to A2, you don't get the UCAS points from it. So you could still start off with 4 subjects and only sit an exam for one, which you then drop.
Also, about how many exams you have, I believe they're combining the ASs and A2s to make up what would have been our A2 papers.
For example, in psychology, I sat 2 AS papers this year, but next year I'll sit 3 papers that cover both years which will make up the A Level.
I think for uni, GCSEs are inevitably going to become more important. But I also think more universities are going to introduce admissions tests to make up for students lacking in AS level grades.