I've been experimenting further and reading through the source code. Again, I still only see the inputMethodQuery and inputMethodEvent functions as entry points to potentially return a QVariantMap with a "returnKeyType" property, and neither one can be overridden.

I tried creating an inline function in my QML code for a TextEdit/TextInput, but the meta method created has a QVariant parameter instead of a Qt::InputMethodQuery, so the logic from QInputMethod does not go through this function.

It looks like the android code completely ignores the ImPlatformData value (at least as of Qt 5.3.1 where I am based). It may be that this was only ever handled in iOS logic previously? If that is the case, then I will have to abandon this effort and wait for Qt 5.6 to come in with native support for returnKeyType. Unfortunately, that will be too late for this project release.