As I understand it, the end goal is to provide a system that works not only for talk pages but also pages that contain "discussion components and non-discussion components". Would it then be implemented in a way quite similar to transclusion ?
If as described threads can be associated to a page (not necessarily unique), say Foo, then we should be able by a magic word such as {{#Threads:Foo}} to have a transclusion of threads associated to Foo, with various rendering options.
A talk page could be hardcoded in a manner equivalent to show the editable wiki talk page itself, that is the header, followed by {{#Threads:Talk:Foo}}, with the desired rendering (in preferences). It wouldn't do to have {{#Threads:Foo}} because we would need in numerous cases such as processes or noticeboards a threads flow for the page (for the process itself) and the talk page (for meta discussion). (This is still assuming that talk pages have an existence as a wiki page themselves.)
Then we could have complex processes where we would put {{#Threads:Wikipedia:Foo}} where we need to have it, and we could have different ones transcluded on a same page, such as {{#Threads:Wikipedia:Foo/A}}, {{#Threads:Wikipedia:Foo/B}}, etc (effectively associated to a subpage, but this isn't important, an alternative would be options). We could ask only for threads from a given date or the last n days, e.g. {{#Threads:Wikipedia:Articles for deletion|date=7 July 2013}}.