> You can just drop any old JS library and write a port for it (it will be async, though).

Actually, it's pretty simple to wrap Javascript functions so that you can call them directly from Elm. See e.g. [0] which is called from Elm here [1].

[0] https://github.com/elm-lang/core/blob/master/src/Native/Colo...

[1] https://github.com/elm-lang/core/blob/master/src/Color.elm