thoughts from a developer. Author of Hands-on Mobile and Embedded Development with Qt 5 http://bit.ly/HandsOnMobileEmbedded
Qt for WebAssembly on mobile devices, specifically phones, has lacked an essential feature - support for the native keyboard. It may or may not have worked. If it worked, it did not work very well. The tricky issue is opening the keyboard when needed and closing when it wasn't. There is no simple API for doing that on any platform we target - iOS, Android and Windows.
Although it feels a bit hacky to me to open the keyboard using javascript , we use Emscripten's C++ interface to create a hidden javascript text input element and set focus to that, which opens the platform keyboard.