Serving Cloud Assets over SSL
Personally, I would just go with S3 (I've ranted about this before), but I understand that sometimes your hand is forced.

I was not even aware that Rackspace supported SSL or that it would be a different domain. I did some digging through their docs and it seems there'll be some work involved to get this feature in and it will cause a change in behaviour, so I'd say this will have to wait until 2.2.