Making some assumptions like the OP intended to write 'again' at the end of his subject line and that the rules don't change perhaps the discussion should be
'If you were looking to build a car to be competitive in the championship would you ever choose a bike engine?'
I think the answer is no. A competitive car needs a lot of downforce, therefore it needs a lot of power. A Hayabusa and a Cosworth XB have roughly equal cylinder capacities but the XB has much larger valves and a larger bore. That means it can flow more air and therefore make more power. And there is not a lot you can do to the bike engine to change that.
There are some XB internal photos at
http://www.lolachampcar.com/Cosworth%20XB.htm with some Busa parts for comparison.
And of course the XB is not exactly modern. It is though very practical.
Paul