From the photographs it can be seen that the general lines of the TR7/8 have been retained but subtle changes have been made. The controversial rear window line has been modified to incorporate the "flying buttress" shape similar to the Jaguar XJS. Similarly the roof line has been modified to include a "T" bar and removable roof panels, leaving a "Surrey" type rear cockpit similar to the TR4. I think this type of design would have been well received in the 1980's and 90's.
But what of the power unit, I feel there would have been two alternatives, the "O" series four cylinder engine in the '7 and an uprated version of the Rover V8 engine in the TR8. In either case they would have been equal to or ahead of the competition.
Sadly we will never know.