Meh, we will see. Theyve been blathering on about a Z10 for years in Motor Trend, and nothing has been confirmed or denied. The last "concept" drawing I saw looked like a mishapen Z4 Coupe crossed with an M6, not a pretty looking car. Motor Trend is convinced that BMW is working on it after an interview with their product development guru Burkhard Göschel said that there would be more done with the M5/M6's V10 in other products...
IMO: I'd like to see BMW get compeditive and build a super-dee-duper sports car, but I think they should stick to something like the Z8. Going for a mid-engined supercar looks good on paper and sounds good when doing some armchair racing, but a front-engine RWD coupe would be cheaper to produce, cheaper to sell, and probably easier to drive on the street.
If anything, BMW should set it's sights on the SL65 and SLR, not the Gallarado or F430. They can make the car as capable as they wish, but they also cannot negate the fact that it will probably sell to wealthy business men looking for an expensive and sporty daily driver. That was why the Z8 was so awesome, she looked good, drove better, and could be a daily driver if the owner wished.