"Anyone Fancy a Twin Air lump in a bike frame ??"
Short Answer - No
Long answer: well, it's a 0.9l unit that outputs 105HP. Comparing same cc, for example Ducati 899 Panigale (898cc) is 148HP. Also, with bikes it's nice to have a smooth-ish power curve, while with a turbo you get a bit of a laggy low-end. I'm not sure what size the Fiat engine is either, could be bulky with turbo added, or maybe not?
In any case, bikes achieve high power from small(ish) engines by revving a lot higher, that in turn places more stress on components that need to be more carefully engineered / have better quality materials than car engines that redline at 6 or 7k.... which is probably why the Ducati costs almost £13k, more than quite a few small cars