I run Zwift on a Surface Pro 3. It is mounted on an arm such that it is suspended in front of me as I ride but it is not connected to its keyboard. Since it is running the PC version of Zwift but has no keyboard, I am unable to access several Zwift features, such as U-turns, camera angles, group messages, etc. unless I separately connect a phone.
It appears you have worked out a touch screen only GUI for iPads. Perhaps you might find your way clear to create a similar GUI for PC tablets.
My suggestion is to use the mobile app along with your Surface Pro. It includes the features you are looking for. I’ve used it for a PC, a Mac, and now with Apple TV, it works flawlessly. It eliminates the need for a mouse and keyboard. It will pop up with a keyboard when making comments; works in iOS and Android.
With the huge number of options users have for hardware on Swift, I doubt they would invest much resources for PC tablets, I’d think it’s a small % since generally users will be using something with more GPU power. It’s amazing they they are across the platforms they support.