I wouldn't mind seeing different speed limits for different lanes. Example: 100 in the right, 110 in the middle, and 120 for the left lane.
Another idea would to use the orange speed signs, which represent recommended speeds, with the standard speed limit signs. So the orange sign would say 100 recommended, while the white sign would say 120 maximum.
I would think that having different speed limits for different lanes could cause some problems for people moving from 1 lane to another. There's already enough trouble with people merging from an on-ramp doing 90 when traffic is doing 120.
I would think you'd be better off saying "trucks stick to the right lane, except when passing", leave the centre lane to slower moving cars, and the left to fast moving cars. It's more of a road education issue than a speed limit enforcement issue.