It's nice to finally see an option for faster uploads. With a couple of Slingbox Pro-HD's you really need more than 2Mbps. 5Mbps should suffice, but only if the speeds are very stable, and then there is the issue with the caps if you try and stream too often.
My $95 FiOS service is very nice for uploading high quality video. I assume that Comcast will have to lower prices for the 50/10 service where FiOS is available if they want to compete. So, I would not expect the Comcast "Extreme 50" tier to cost $140 in all regions.