Thanks for describing your use case in detail, @Phil_Burapha!
Given that your underlying need is for computing a median, would a median function work for you? I don't see any such thing in core XPath/XQuery/XForm but I do see that MarkLogic has a custom median function: https://docs.marklogic.com/math:median
I can't find a reference to an XForm sort function, do you have a link? I see this article about an XLST-based alternative (wouldn't be supported by ODK tools). It looks like Orbeon Forms has a custom function.
Thanks for pointing to that spec proposal section, @danbjoseph! We don't do formal voting these days and should update that. This thread is a fine feature proposal and will be helpful for gauging level of interest/need.