i don't see why it wouldn't work, I'd probably depend on some stronger magnets than what you'd get in a smart cover though.
So I had this idea the other day after weeks of trying to figure out how to get my iPad to stay in the dash. Magnets? I was going to take apart one of those smart covers and embed the magnet into the dash. So when it is slid in place the magnets will help keep it stable. I did a search for this but couldn't find anything. Has this been done before
Check out my setup. It's funny that you describe exactly what I ended up coming up with, but I'd never seen your post before!
Definitely depends on your dash layout, and the magnets wouldn't hold the iPad by themselves, but with a few rubber feet in the right place, it's been a perfect setup for me.