Now, this could well have changed in the last 5 years. A quick Google scan doesn't really show anything definitive one way or the other. If I were really dedicated, I'd at least call Yosemite and see if they've gotten any of theirs to work.
The best modern system in Yosemite that I'm aware of is the composting system in Little Yosemite Valley, and a smaller one at the top of Nevada Falls. If anyone has used these they probably had a surprisingly good, mostly odor free experience. They have an old model at Vogelsang High Sierra Camp (10,000ft) that was basically a holding tank, bad design and lack of maintenance. For the challenging locations at higher elevation, the best example is Long's Peak in Rocky Mtn NP (a popular 14er with similar usage as Whitney). This has all been discussed in previous posts, but at the bottom of this post is a link to the a report by a National Park Engineer Joe Arnold that describes about 30 years of successful toilets at a higher elevation than Trail Camp. At these difficult locations, a solar powered dehydrating system is the way to go. The history of success with the toilets at Long's Peak proves that it could be done at Whitney where we have more sunshine than Northern Colorado.
For any toilet system, especially at higher elevations, it takes dedicated staff to perform regular maintenance to make it a success. The best design in the world would fail if it was not kept up. So the only way it would work at Whitney would be to get full buy-in from the people required to maintain it. The current generation of Whitney Rangers struggled horribly with the crappy designed old toilets and they are probably scarred for life about this. At Long's Peak, they use Llamas on a weekly basis and the task is not all that bad. No helicopters. The Llamas are very popular with the hikers and it gives them a chance to meet people on the trail and teach the ethics that Laura and others are screaming about (understandably).
And for those who love wag bags so much, go ahead and use them all you want, at home, on the trail, at the office, just don't force them on everyone else as the only possible solution to a difficult problem.
Performance Evaluation of Backcountry Toilets 
