Now that I've used the SP4 for a good 30 minutes, I've changed my opinion. The new SP4 type cover is vastly improved over the old one. I could use it as my primary input device.

In fact, I think it's actually a problem for MS! :) The reason why the Surface Book was so appealing was partly because the keyboard/trackpad just wasn't that great with the SP3. Now that they've improved the type cover so much, the SB seems less necessary.