They probably haven't come close (it's a 1st gen title after all), but it may still not be possible to add shadows afterwards without seriously re-jigging how the game renders things, re-writing shaders etc, which probably would be expensive and thus won't be a very high priority post-launch. (My baseless speculation; take for what it's worth lol.) Just look at all the advancements needed to get Doom3 to run at 60fps on the old consoles.
I don't know, after the post launch 1080p patch from ACIV it makes me think anything is possible lol. They probably already have the shadow system running in the engine but simply switched off, maybe they'll find enough juice after a short while just like Ubi did with AC for a patch. Who knows, but it's a good sign since it's only a first gen title so the chance of that happening does sound optimistic.