Would it work to retard sourdough in bulk? Or only after it is shaped? Why?
Yes, you can retard it in bulk. As long as at some point it gets a chance to ferment, it should be fine.
One of my favorite wintertime sourdough recipes involves mixing the initial dough with very little starter and then putting the entire bowl of dough in our "cold room", which isn't as cold as a fridge but is much colder than the rest of the house. In there it goes through a looong slow rise -- as long as 18 hours -- and ends up extremely sour and delicious. So give it a shot and see what you end up with!
does it work better if it is bulk fermented before the bulk retard?
As Floyd said, your dough has to ferment in bulk. This can be before, during or after retardation or any combination. This assumed cold retardation in the fridge at around 40 dF. If you are retarding in a cool room, say at 50 dF, more fermentation will occur during retardation.
At the San Francisco Baking Institute, I was told retarding in bulk is better for high hydration doughs and retarding formed loaves is better for low hydration doughs. Note that, in commercial bakeries, they have retarding cabinets which are generally at 50 dF.