This sounds a bit like our Owner Maintenance category. The govt washes its hands of us "older out of production" aircraft.
The owner does the sign off as it would be difficult to find an engineer to sign it off when who knows what has been done to it. My experience engineers have no problem working on these as no signature is asked.
The only stipulation is you can't violate the original type certificate ,,,,, unless it is signed off by the minister, or his designate. So yes I can put a PT6 in my Grumman, it just needs to be engineered

Will open up a whole new world for private aircraft.

The only thing holding people off in Canada is the perception it will decrease the value. Not proving to be the case.