I stopped at Lowes and looked at the mowers they sell. All the non-zero turns are rack and pinion. There is a rear engine rider with a self contained unit on the front axle. Pretty neat set-up.
With this being said, an after market rack/pinion unit is really just improving the stock set-up.
I'm not sure why this ever became an issue or why uslmra doesn't allow it when it does seem to be allowed in the smaller groups around the country and is legal to run in the larger National organization.
My thoughts...
Tom