more details on the "sled" type I am considering
here's one in action:

more info here
http://www.skipulk.com/index.html I also have no intention to "ride" any sled downhill - the pull system uses poles so you keep the sled behind you (it pushes against the harness).
Whitney may not be part of my route - been there, done that. I may hike in/out at Horseshoe Meadows instead. going north, I save myself the killer climb with full gear, while going south, I don't have to worry about the crazy descent, although southbound I'd probably do Whitney as the destination over bypassing it.
thinking out of the box - happens when you have more than a dozen summer and fall JMTs behind you, plus, it would be something very few have done before. Searching online, I have found some info on skiing the JMT from about 15 years ago, so few ever try this. Even that report showed some snow-free valley bottoms, so the sled may have to be small enough to just unload the pack where it makes sense.