The busiest speculating German magazine (Autobild) created those drawings some weeks ago:
As always they will have no idea how it will look like, but this is no reason for them not to draw it.
They say that it will be a sportier alternative to the Mercedes SL, produced from 2010 to 2017, about 15,000 cars every year. Prices in the area from Euro 80k to 100k. Low weight, and a lot of high tech (for example a transparent folding roof that can be obscured). Asked about a Z8 (or Z10) BMW said "We are thinking about it".
By the way, since 2004 Chris Bangle is not responsible for the BMW design any longer.