If this was an education-level device, there are all kinds of possibilities. Perhaps a polycarbonate case as some have suggested. No need for external monitor support or some of the other features you get with an MX chip in an Air. What about a touch screen as a way for kids to transition from an iPad and iPadOS to keyboard? Or running a version of iPadOS in the first place?
Apple hasn't been making lower-end education devices (like the iBook and eMac) for a while, but they may want to get back into this market just so students grow into the Apple ecosystem, as opposed to being raised on Chromebooks.
Basically we don't have much more info than a chip, though, so so it's all speculation at this point.