ok, well I went ahead and did my own custom template to accomplish this, a bit tricky to get it working given it uses custom taxonomies etc, but seems good now… I ended up using the question “tag” field to store the “subcategory” for now as it seemed the easiest way to accomplish this to begin with (but in the end was a lot of custom coding anyway.)
I then created an alternative loop at the bottom of the existing questions list template to loop through each parent category – and then each subcategory in each – and list out the questions with a matching tag value for that subcategory and put them in accordion/metabox style dropdowns.
the disadvantage of this is losing out on having tags for questions at this stage, but I don’t really feel they are needed at the moment (or if at all for my purposes, I much prefer the advantage of having appropriate subcategories myself) and I can always add them back later.
anyway if you want to see the result or to get in touch if you are still wanting to implement something like this (and/or if that bounty is still up for grabs, lol) … in case I lose touch with this old thread like you may have already anyway, you can do so here:
https://pluginreview.net/support/
(this is gonna be my new support forum for my wordpress plugins.)