You're forgetting that from the iPad you also delete a touch screen digitizer and whatever tech makes the Apple Pencil work. You also drop the rear camera and flash, loose the Centerstage camera for basic 1080p and you don't really need 6-axis motion sensors, but I think that is baked into the A Series SOC now. Also 14-ish-inch screens with a 2.5k horizontal resolution are probably a bit more commodity than the display in the iPad mini. Also, they can ditch the glass laminated display on a low end laptop. In any case, there is a lot to delete before adding back laptop parts.While I would love this, I have to consider how the current iPad mini with its A17 Pro chip and touchscreen but no keyboard costs $499 retail. Assume that a laptop chassis with mechanical keyboard and a larger screen (12-13”) and battery has to cost at least $100 more, maybe $200 irrespective of the OS running it.
If Apple is after the education market, they need to come in under the cost of an 11th gen iPad with 256GB of storage and a decent keyboard case. So somewhere around $550 - $650. Given the $499 education price point of the Mac Mini, I think $650 for a less powerful laptop is a good fit too.
An A18 Pro powered Mac would probably be quite capable. It has a media engine and a ProRes accelerator which means it'll probably run iMovie and Final Cut Pro better than any Intel based Mac and well enough for social media and edits for school. The 6-Core GPU would be plenty for 2d design/illustration apps and basic CAD/CAM software too.