I can see there would be a place for a longer school day, but only once children are in secondary school. I Think it could help to provide more extra curric activities to all students, rather than those who naturally sign up for everything because that's just the way they are!
Also I would like to see the summer holiday reduced to 4 weeks, but with an extra holiday brought in say after 6 weeks, so overall 1 week less over the year, but split a bit more evenly.
However, it would need to be properly funded, and more teachers employed.
I doubt it will ever happen though.