I have no windows touch device to test, but according to this post, there should be something about touch events in since 4.14. Did you verify that you get events from more than one index?
You may check how far you get by putting breakpoints in the code at the following locations and check if TouchIndex>0:
- Start in “\Engine\Source\Runtime\ApplicationCore\Private\Windows\WindowsApplication.cpp” - Line 2203 / WM_TOUCH (4.25 version) to see if the application is receiving multiple touches from windows api
- “\Engine\Source\Runtime\Slate\Private\Framework\Application\SlateApplication.cpp” - Line 5671 OnTouchStarted() and OnTouchMoved()
- "\Engine\Source\Runtime\Slate\Private\Framework\Application\GestureDetector.cpp - GenerateGestures() - This indicates, that no more than long press is recognized inside the engine and it was meant for Android according to the changelog, so not sure if this will get called on windows.
That at least should you get to the point that multiple input touches are recognized. Although it seems that real gesture detection is not handled by UE4 for Windows yet, which is perhaps a bigger task. The event WM_GESTUREis not handled in WindowsApplication.cpp, which leads me to the assumption.