For SP4, please bring back native 16:9 1920x1080 resolution - whatever size the screen. As a very happy original Surface Pro 128 user, I was disappointed to see the new Surface Pro 3 3:2 screen ratio 2160 x 1440 res. Although this may be "higher" res, we live in a 16x9 world, every HDTV, PC, movies, etc are designed for this. For photographers, Surface is great for full screen 1080 pics and video, and why change to anything else until we reach 4K (which really isn't necessary for screens of this size yet)? I would love a slightly bigger screen, but within the 11 and 13" range and 16:9 only please! If they can do this and keep the keyboards backwards compatible, that would be great. But those accessories can be improved and one day the old ones won't exist anymore. Of course, the usual processor, cooler, thinner, latest wifi/bluetooth, etc upgrades are to be expected. I agree with whoever said 128GB should be minimum for Pro. IF possible, a second USB port would really help. This is one of the only things keeping my Surface from being a complete desktop replacement (and just a little better GPU/games performance but that is getting closer). I could add more to the wish list, but screen size, more GPU/processor, and 2nd USB port are my top 3 requests. Other things like fingerprint scanner and waterproofing, while awesome, I think those costs might outweigh the demand.
I still stand by the original Surface keyboard 'touch' version - it has the best mouse/touchpad of any model since and does not suffer the two-handed/right clicking issues. MS needs to research this, I would buy a newer keyboard but the "both hands" mouse right clicking still has problems, I believe even with the Surface Pro 3 era keyboards.
Wish lists aside, MS knocked it out of the park with Surface Pro, possibly the best computer I've owned. I attached a pic of Diablo 3 running on Surface Pro, into the Xbox One, using Bluetooth Logitech devices on the couch. I was technically playing D3 on Xbox One before it was released
No other tablets can do this that I know of.