The problem is, low budget machines running Windows are really really bad. I just cannot see a $329 surface running anywhere near as efficient as the iPad. Hopefully they prove me wrong, because I would definitely buy one for work.
This is the main issue. Sure, a full 10" Windows 10 Pro device for $400? Sounds great, but I'm assuming the $400 will be the 64GB model, which will be pushing your storage limits from the start ... then I believe you need a minimum of 8GB RAM to run Windows smoothly, and no doubt the $400 model will come with 4GB. Also, for $400 I highly doubt you're even getting an i3. So yea, ideally this is great, but in practice I can't see it being a smooth Windows experience at the $400 price point with that parts you'd likely get, unless people are using it strictly for email/web browsing/youtube.