A 4 cylinder turbo with upwards of 200bhp? I see nothing wrong with that and i pretty much guarantee you it wont be US only! There's a reason the most popular E85 Z4s, SLKs, TTs etc in Europe are the 4 cylinder ones.
Plus i dont think that engine would replace the 3.0, it will probably replace the 2.5 six as the base engine in Europe and IF they sell it in the US it'll probably be sold alongside the 260hp 3 litre as a new entry model..
My opinion as always but i think it makes sense.