I thought that the year-round model wasn't to increase the days in the classroom so much as get rid of the three-month gap(replacing it with several shorter ones) because students tend to lose so much knowledge during summer vacation.
I've heard proposals for both bandied about. Some suggest that we ought to go year round "like they do in Korea" [sic] to get more learning in. Others just want to space out the breaks more evenly, as you suggest.