While I was waiting for a response to my first post, and to my emails to Jay Alberts and Angela Ridgel, I did some more "research" and realised that the answer to my main question was obvious. And the answer is ... it's too soon to tell !

Similarly, if the Parkinsons researchers haven't (yet) studied the application of interval training techniques to high-cadence cycling, they can't (yet) know much about the comparative effectiveness of this combination.

The penny dropped while I was reading a relevant (and recent) paper. I've summarized it by extracting a couple of key paragraphs.

Ridgel AL, Phillips RS, Walter BL, Discenzo FM, Loparo KA. Dynamic high-cadence cycling improves motor symptoms in Parkinson’s disease. Frontiers in Neurology 6:194 (2015) doi: 10.3389/fneur.2015.00194

"The dynamic cycling paradigm that we developed uses a motorized stationary cycle to assist individuals with PD to pedal at a cadence faster than they can (or would) pedal on their own. In addition, this rehabilitation paradigm is unique because the motor rotates the pedals at a high speed with a slight, but prescribed, variation. These dynamic changes in cadence appear to be an important component of tandem cycling. [A]" [B]
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"CONCLUSION: These findings show that dynamic cycling can improve PD motor function and that activation of proprioceptors(1) with a high cadence but variable pattern may be important for motor improvements in PD."
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"Funding: This work was funded by a National Institutes of Health Grant R21 HD068846 to Angela L. Ridgel."
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"Conflict of Interest Statement: Provisional patent filed through KSU on 12/2014; full application has not yet been submitted; no royalties have been distributed."

[A] Ridgel et al. Variability in cadence during forced cycling predicts motor improvement in individuals with Parkinson's disease. (2013)
[B] Ridgel et al. Forced, not voluntary, exercise improves motor function in Parkinson’s disease patients. (2009)

(1) In the limbs, the proprioceptors are sensors that provide information about joint angle, muscle length, and muscle tension, which is integrated to give information about the position of the limb in space.