I think that's for all Z4 models. I remember seeing stats for previous years where it was just over 3k sold per year. Anyways, I think the new engine is quite good personally.
I too share rking's concern that BMW will just chop the line if the sales drop too low.
E89 Z4 sDrive35i 7DCT "Zayna", Alpine White/Coral Red
E92 335i 6MT "Calixta", Space Grey/Coral Red [Retired]