[southblue]

Series averages were at an all time low during BB10 (2.5m). It could be argued that this is the number of core fans that the show attracts. I believe that without extensive advertising, BB12 will probably only attract this core group of fans.
Having said that, running the Celebrity version first could prove fruitfull (as this tends to attract more casual viewers). However, without a couple of big names, this could be a risky strategy as many fans prefer the main show to the Celeb version.
These two factors may cancel each other out though. So I predict a season average for CBB at around 2.5m (with launch night and final night perhaps topping 3m)
I think the success of BB12 very much depends on the popularity of CBB. But as a guess I would say minimum 2m and max 3.5m with an average of 2.5-3m.
Just a guess mind