>> Maybe like there is a variable other-window-scroll-buffer,
>> it would be nice to add a new user option
>> other-window-for-scrolling-function that will return
>> a window for scrolling.  It could provide a choise list that
>> includes a function that returns the most-recently-used window.
>
> Maybe a variable 'other-window-scroll-window' whose value could be a
> function to get that window.

Since there is already the word "window" in the function name,
maybe better would be 'other-window-scroll-default' that hints
that it overrides the default that is the next window: