It would look something like a Volvo 240 - utilitarian, maybe even boxy. It would have a basic, powerful-enough 4-cylinder engine, installed longitudinally, mated to either a five-ratio manual gearbox or a mechanically-controlled automatic gearbox with a locking torque converter, driving the rear wheels (with all-wheel-drive as an option). It would have a slew of airbags, crumple zones, and all the necessary safety features. Four-wheel disc brakes, ABS, all that good stuff that helps you avoid crashing in the first place. It would have all the usual OBD-II diagnostics, as necessary these days for legal reasons. The throttle would be controlled by a cable pulling on a spring-loaded butterfly valve.
It would not be the average car, though. It would, as standard, not have power accessories. No power windows, no power locks, no power seats... optionally, yes, but not on the base model. Power steering and power brakes, yes. It would also have a feature not commonly found on OBD-II cars: no reader would be required to get codes. There would be a readout under the bonnet to get the codes, and an explanation of the codes in the owner's manual. This would be a utilitarian car, designed to get the user from one place to another with a reasonable amount of stuff, and to be easy to fix. Tool-less replacement of bulbs, a basic toolkit included, and the aforementioned code readout would make it more appealing to the hobbyist.
Of course, it would never sell. People, in general, don't want a car that assumes they're competent at wrench-turning. Those who do are an exception, and not a unified market; while there are plenty of Volvo-enthusiast hobbyists, there are just as many people who tune hot rods, classic American iron, and so on, and there's less crossover than I would like. Just try to sell a reborn Volvo 240 to a Corvette fanatic!
But if I ever win the lottery, inherit Bill Gates's millions, or somehow come into possession of that sort of money, I'm definitely going to attempt to license the designs for the Volvo 240 and its red block engine, and bankroll this.