Yes, regenerative shocks have been discussed. There is an company that spun off of MIT called
Levant Power that builds a hydraulic regenerative shock absorber, and the Illuminati Motor Works X-Prize team built some (similar to the article you posted) along the way to the contest; though they discarded the idea because they were not providing enough dampening.
I think that regenerative shocks would be even more effective if you used them in conjunction with more rigid tires; that were non-inflated. Normal tires absorb most of the small bumps, so having a rigid tire (similar to the Energy Return Wheel) that had lower rolling resistance, and it would pass more motion through to the shocks. So, the ride would be similar, but the dampening work would be mostly done by the shocks, so you could regain more energy, as well.
This is the second stage of efficiency improvement that I hope to be able to try on my CarBEN EV5 project: rigid airless tires combined with regenerative shock absorbers.