So, the extend/trim tool doesn't show up when editing walls? Brilliant, I cannot find this stated anywhere.
Also, I had watched videos and specifically, the "recommended" video on extend and trim and the presenter was using a polyline on rafters, I believe. I had tried adding a polyline to the exterior wall, just in case I needed this, but "walla", still no extend/trim for the interior wall.
So, "Chief's" solution to extending walls is by dragging only. Sign me up for X12 then!