Honestly, i think this would be a good idea. If there are wheels on the market (like XBox360) that support vibration and FF this would be great! Of course it should not be canned effect, but "real" according to engine revs and wheel/surface condition. Imagine the vibration when running with a flat tyre or with a bent suspension.
Conclusion:
Canned vibration effects: -1
simulated according to road and car conditions: +1
... but this should be moved to improvement suggestions