Compulsory gap year?
Bad idea for the many - I would think the majority - who can cope absolutely fine with the current system, and who are ready for university on the current schedule. As I said upthread, the option of a gap year is already there for those that want it.
I would be in favour of degree programmes lasting 4 years
There already seem to be a lot of integrated Masters on offer. This is pretty much the norm for engineers, but there are lots in other STEM subjects. However - DH took a look at the syllabus for the MSci at the uni where we both did our BScs and PhDs, and he thought the content was pretty similar over the 4 years to what we'd done in 3.
There are quite a lot of foundation year courses available in some fields. Maybe those should be commoner, and compulsory for anyone who really doesn't have the grades required to hit the ground running. This seemed to be how the engineering degrees DD was applying for worked, plus if grades weren't high enough after the first or second year of the degree proper then they'd leave at the BEng stage.