Great points. My son was in half-day K, but because they have more full-day students, the half day kids were expected to keep up with the full day curriculum. This meant scheduled recess only on Fridays, and that only actually happened about once a month due to assemblies and precipitation/cold weather.
They spent the day sitting and working at literacy and math centers, reading groups, writing in journals, doing math and more writing. A and C days had gym. B and D days were either art or music. Library time only came every other week at most.
My son actually said early on in the year that he liked kindergarten much better than preschool because in preschool you just played and in K you get to learn. He would get annoyed at the kids that talked over the teacher.
I don't think going to a full day where he'll get a recess or two every day will be a problem for him. And I don't know if the Full-day kids sat as much as they they did, but the idea of sitting and working won't be new to any of them.
While academics is important, the big reason I'm looking into this is because of the social aspect. Maybe the 1st graders will be less immature and less likely to be annoying than they were in Kindergarten, but I don't know.
I don't think the principals are trying to push me off the idea by suggesting a skip next year instead of this year. I just want to think it all through before I agree to waiting a year for a skip.