Sol, this subject has been discussed in other threads, but to address your question seriously: these are rumors only. I've only read comments from one forum member who claims inside knowledge that such a bike is coming, but he hasn't given anything to back that up.
The current 848 is raced around the world, and makes a superior road bike. A change to an extremely short-stroke engine would take away some of the beloved midrange in search of higher top end, which isn't so useable on the street. To retain the midrange you would need to up displacement which might rule a mini Panigale out of most racing classes. SO, to be successful with an engine switch Ducati would have to maintain the midrange AND increase the top end WHILE keeping the displacement at no more than 848cc. A tall order.