How about the window scroll events?

[Pickachu]

Maybe it's intended by design. But how about using it to monitor window events?

Something like:

<core-scroll-threshold lowerTrigger="0"></core-scroll-threshold>

var element = document.querySelector('core-scroll-threshold');
element.scrollTarget = window;
element.lowerTriggered = function () {alert('yay! ');};

It seems to fail because window does not have scrollHeight, but scrollY property.
And here it uses only scrollHeight: https://github.com/Polymer/core-scroll-threshold/blob/master/core-scroll-threshold.html#L165.