Surprisingly there are only 29 comments. Maybe we just need to make more noise?
As Emmanuele Bassi noted, “making noise” is not useful, quite the contrary. One of us (the people who care about the topic; it could be someone from MyPaint, from GIMP, maybe Carlos who manages Wacom tablets on GNOME… or someone else) will have to implement it at some point if we really want it.
Personally I can’t make the time for this right now since Windows is not my platform of choice, though I still care (so maybe one day if I get very bored or if I get funded for this).
On the other hand, as @Jehan noted it seems to be common (at least from googling) for people to disable Windows Ink to avoid laggy brushes. SO, even if GDK supported Windows Ink, would it even work well? It’s 2017 and many native Windows Apps recommend disabling Windows Ink? It seems strange, doesn’t it?
This must be one of these cases where you will have tablets working better with a driver while others will work better with the other driver. So it likely means we should just have both implementations and appropriate settings to allow people to test and choose (better would be some kind of detection of what will work better for which tablet/pen, but I doubt such a test can be automatized, can it?).