Because of economics, piston twins will go the way of the B707 and the flight engineer. Upgrading thirty year old junk can only go on for so long, modern airspace requires sophisticated equipment to operate safely in it, eventually the cost of modifying a 1970s aircraft to accept 2000s technology becomes prohibitive. Try fitting TCAS, GPWS and RNAV into an aircraft designed before these things were even dreamed of.
The new generation of pilots coming through will need TV screens and sophisticated autopilots, don't expect them to be able to hand fly an NDB approach on round dials any better than we could fix our position using a sextant.
Eventually the insurance companies and regulatory authorities will accept single engine risk vs the severity of a mis handled engine failure accident in a multi. At one time long haul airliners had four engines, now with increased engine power and vastly improved reliability twins are the norm.
There will still be some piston twins for niche market work.