I am willing to bet a large sum of money that the next M3 won't have a TT V6. BMW has done some things that are questionable in the last few years however I don't think they are going to abandon inline sixes for V sixes now or down the road. They make the best inline sixes in the world, I am quite sure they are going to stay with what they know.
2011 E90 M3 ZCP - Individual Moonstone/Individual Amarone Extended/Individual Piano Black With Inlay:LINK!!!
1994 Euro E36 M3 Sedan - Daytona Violet/Mulberry:LINK!!!