Another problem with this idea is that there can be a decent amount of faculty sharing. All your professors don't work for the 'school of medicine.' Your cell bio professor has responsibilities (and classes to teach) in the dept. of cell biology. Your anatomy professors have other classes and duties as well. All of you classes work this way. I doubt these departments would be willing to outright give their faculty to the medical school year round.
I'll use the anatomy class at my school as an example. We have gross anatomy for the better part of the fall semester, and it takes up the majority of our professor's time (2 hours of lecture in the morning plus 2-3 hours of lab in the afternoon, 5 days per week, plus lecture prep, lab prep, prosections, and testmaking.) They also do a lot of research during the class, as there are many cadavers dissected and available for the purpose. So this takes up the majority of their fall. So why not just do the same in the spring? Because that's when they teach anatomy to the PAs, the CRNAs, the ODs, and all the rest of the health profession classes. There literally aren't enough hours in the day, or space in the gross lab for that matter, to have the medical school AND the other health profession classes going at the same time year round. Other courses would probably have similar problems. Could they make it work? Sure, but it would require a huge investment in hiring more faculty, expanding facilities, etc. If you wanted to increase the total enrollment, it's much easier to just make the single class you already have bigger. Running a few more scantrons through the scanner a few times per semester isn't nearly as big of an investment 🙂 So, while this would be a good thing for the students, there is NO upside for the school that I can see.