A Windows 10 Mobile version that will run on a Raspberry Pi SBC. I don't see it ever happening, but I'll keep asking for it anyway. Windows 10 IoT just doesn't do it for me.
Control the bandwidth that Microsoft uses to download updates.
When they pushed a large update onto my PC, it tied up my DSL connection for the better part of a day, and I couldn't get any work done for my clients.
Windows 10 seems to be imitating the push model of smartphones--but Microsoft forgot that many of our desktop PCs don't have 4G LTE bandwidth. All I have is DSL.
BitTorrent lets you specify the bandwidth allocation for each download and each upload. There should be a similar setting for Windows updates. I need to give my own clients' jobs higher priority over Windows updates.
Make the Action Center area smaller.
It makes no sense for those of us who only get a few notifications per day in that area to have a three-inch-wide immovable stripe running down the entire length of the screen. It could be a popup window instead that you could move around and resize.
Make it possible to "float" Live Tiles onto the screen the way that Windows Gadgets worked in Windows 7. Unlike Windows 8, Live Tiles have been reduced to an area that you can only see by selecting the Start Menu. Otherwise, the Live Tiles don't appear. What's the point of Live Tiles that update when you can't see them?
One elegant way to do this would be to allow Live Shortcuts. Put a shortcut to the Weather Live Tile on your screen and let the shortcut constantly update with the latest weather info. This would be similar to how Widgets work on Android.
Independent and saveable desktops for virtual desktops.
Live Tiles are about as useful as a Screen door on a Submarine. It is just like when Microsoft though that everyone needed Gadgets on your desktop that you will never see. Just like having wallpaper that you will never see, because your open window covers it.
Drop all of these gimmicks and all Operating Systems would fly.