In the districts I'm aware of in Mississippi that have made this move, over 95% of teachers have been in favor of the change specifically due to reducing burnout.
Not sure about the pre-adulting summer, but not sure that couldn't be made up in the weeks off.
The way our district is approaching intersessions (and the way districts we've modeled after are doing it) is that on the 2-week fall break and the 2-week spring break, the first week is called "intersession." During that time, students who need additional remediation from the 9-weeks before or the additional prep leading into the next 9-weeks can get much more personal attention. Additionally, teachers or community groups who want to offer other, non-curricular opportunities (sports camps, "adulting" classes, etc) can offer those during the intersession.
Teachers are able to volunteer to work on the intersession week for additional pay based on the number of students signing up to participate during that week (but the teachers absolutely do NOT have to volunteer). The districts we've researched have said they've had to turn away volunteering teachers due to more teacher availability than students participating, so there's not pressure from the district on teachers to work away their extra week off.
We will run buses and cafeterias during the week on a limited rotation to account for the fewer students who need those facilities.
I'm a bottomless pit of information on this topic at this point, as we've been working hard on the implementation of this for basically this entire school year, so if you've got more questions, ask away.