I predict that by, say, courses starting in 2017, most schools will have ditched the AS completely. This will allow them to teach right through Lower Sixth year and not lose a huge amount of time for revision and exams. Schools will do their own internal mocks to assess progress, as they did in the past. Some independent schools have already announced they will do this from 2015 for those subjects where the new A levels are already available. (Sciences, computing, english, history, some others, not maths.)
However, this will probably mean an increase in university pre-testing, which is already becoming a bit of a nightmare as different universities require different tests and it's very difficult for schools to provide adequate support for all of these.
There is research evidence that suggests that GCSE performance is a more accurate prediction of success at university level, than AS performance. So it is rather strange that so much is based on AS performance. Cambridge, in particular, want to know the exact UMS marks scored for each module.
In the meantime most exam boards have developed co-teachable syllabuses for AS and linear A levels, so it won't be very different from now, except that students will have to revise two years' worth of material for the final exams and that they won't have any grades or marks "in the bank" as nothing carries forward.