Personally I question the value of having Q&A work differently from the rest of the site. The section is probably best served by using the same internal structure (ie regular root nodes and notes like everywhere else), with a (configurably?) forced note depth of 1 when you look at the root node. Effectively that would work like the section does now: you see a question and only its direct answers. The major difference is that there would automatically be a some notes below your chosen depth indicator where there are replies to an answer.
Makeshifts last the longest.