I have flown some light gyroplanes with very light cyclic control forces.
I see no reason they couldn't use a side stick.
Will save me about 3 or 4 pounds and get rid of one more hazard in the cockpit in the event of a crash.
Steve McGowan uses a side stick in his tandem, "The Black".
I have no experience with the side stick like on the black, but on my second gyro I had an offset overhead stick and one issue I had with it might be of some relevance. I used the Overhead stick to train myself on flying by taking off with the low (regular) stick and switch to the O/H stick in the air. It took some time and I eventually learned to fly it but my particular stick was offset from center so I didn't have to look at it. Inflight, with the ground and horizon, there wasn't much problem with holding it level, but after landing the offset didn't allow for the easy visual ability to know when the stick was centered and the disk was level. Once when there was some wind and after I had landed but before the blades had slowed, I inadvertently let the disk drift off from level and when I turned I could feel the wind coming up under the blades and get my right wheel light. I corrected and everything was fine but I then knew what Doug Riley said about most ground tip overs are most likely "Fly overs" from lack of positive rotor control until the blades slow to an insignificant speed. When first flying with an offset stick whether high or low, it might help to keep that in mind.
In regards to a "Trim Spring".
On my Tandem Dominator, it had a trim spring of about 12#'s of resistance. I replaced it with 2 springs with approx. 6#'s of resistance each. One springs ID is slightly larger than the OD of the other spring.This allowed me to pass one spring inside of the spring. The combined resistance is still approx. 12#, But if one spring should break - the Pilot is only catching half of the load, not al of it. This arrangement also "cages" the 2 springs into each other. In the event of a spring breaking, it stays put and doesn't end up going through the prop.