If I had to pick between road and off-road cycling it would always be the former for me – that type of bike and that type of riding just happens to ring my bell, and the aesthetics of a road bike have a lot of appeal. It would be very interesting though, if a road bike could be developed with just a smidge of suspension.
The movement would have to be in the forks at least, possibly the rear as well, to get the benefit of the wheel or wheels being able to react to the bump or hole and go forwards rather than being deflected. Suspension seat posts are just for comfort – they don’t alter the ride. Some kind of hybrid with just a small amount of travel in the suspension, to preserve the characteristics of the road bike on most road surfaces but that could react to a bad surface, would be very interesting to try. Given the rotting infrastructure of the UK, it would be worth a reasonable weight penalty.