I've been using Sony Vegas for my stereoscopic edits; but now Premiere has all these VR tools are there any workflows for doing (non-360, conventional 16:9 screen) stereoscopic editing in Premiere?
The main reason for using Vegas is that it natively supports stereoscopic, and you have tools that let you change the convergence on each clip (pushing it toward or away from the audience) and do stuff like add floating windows.
You can fib and set your sequence VR settings to be Equirectangular, Stereoscopic, and choose a horizontal field of view of 180 and then apply and use the VR Projection effect's disparity adjustment parameter. When you go to export, the exporter is going to notice that you enabled VR and it will add the metadata to your MP4/MOV exports, by default. You will want to scroll down to the VR section in the exporter and turn off "Video is VR". This is a giant hack, of course. as you noted, stereoscopic is really meant to be part of immersive workflows.