Kind of worried that the AP 2.0 rumors today don't say anything about rear-facing cameras or radar to improve blind spot warning.
I'm not really convinced they need more sensors. The existing backup camera is a very high quality fisheye - likely very similar to the front fisheye that's in the triple camera packaging. Unfortunately, in the legacy and early AP Model S that camera links by LVDS straight into the center console, for screen display only.
The only change you'd really need for either blind spot warning or autonomous lane changing IMHO is to get an EyeQ3 type chip doing object recognition against the feed from that camera.
At this point, I have no reason to believe that newer cars (X, refreshed S) are any different from the older ones we know about above - but this is something Tesla could change at any time without there being much (any?) visible sign that they changed it unless you take the center console apart.