Update: as planned, I’ve created a helper library that makes the gesture events from Hammer.js easy to use with Elm.
https://package.elm-lang.org/packages/leforestier/elm-hammer-events/latest/
Hammer.js is actually doing all the work of gesture detection, and it’s pretty good at it. Now you can use events attributes such as onSwipe, onSwipeLeft, onPress, onRotate etc… in your Elm application and it’s as easy as using onClick.