I think they would be crazy to charge $12 for a super Joey but if they did the incentive for me would be integration. All 5 tuners available to all TVs and one list of recordings and timers.
If you watch the video of Scott interviewing Vivek you'll notice Vivek says the SJ will be a savings over having a second Joey. Sounds like it's the same as a Joey at $7 but I can't imagine Dish doing that, my guess is $10.
If Dish does make the SJ $7 I wouldn't be surprised to see them raise the price to $10 next year. Similar to what they did with the Hopper DVR fee and secondary Hopper fee.