On May 3rd 2016 (post #356) I wrote:
"My reading of recent research outputs leads me to believe that the role played by "variability-of-cadence" (and other factors) will be studied more over the next few years, most likely by Ridgel et al. at KSU ..."

And now, about one year later, this is indeed what seems to be happening.

I've spotted an abstract from a poster-type presentation which occurred in May this year [1]. In the presentation, Ridgel et al. reported on a trial involving a motorized recumbent cycle. During 30 min sessions the cadence was varied in the range of 75 to 85 RPM.

Hopefully a research paper will be available in the not-too-distant future.

[1] Dynamic Cycling Improves Motor Symptoms And Mobility In Individuals With PD, Angela Ridgel & Dana Ault, ACSM Medicine & Science in Sports & Exercise, Volume 49, Supplement 1 5S, p29, May 2017.
Dynamic Cycling Improves Motor Symptoms And Mobility In Indi... : Medicine & Science in Sports & Exercise