Really I'd rather the whole thing was kept in the coding for hint if at all possible, rather than altering other components

Yep totally, I'm pretty sure you should be able to override this function from inside adapt-hint, I think by doing something like

view.getInviewElementSelector = function () {return '.hint-extension-item-body' }

in between the current lines 118 & 119 of adapt-hint.js

If that doesn't work it'll be something like messing around with Text.prototype.getInviewElementSelector

I suspect the inview library is just not getting triggered when you open the hint, forcing a $(window).resize() might do it, if not you weren't far off with doing setCompletionStatus you were just doing it to the wrong thing - it needs to call the text component's setCompletionStatus, not adapt-hint's (which doesn't actually have such a function)