East of the Sierra Crest (ie outside Sequoia National Park), the Whitney Trail passes through John Muir Wilderness. But given that there was a toilet at Trail Camp in the past, I don’t think there are any regulations that bar having a restroom in a wilderness area. With this said, I don’t think that unsightliness was ever the reason for removal of the solar latrine. Rather, from what I have heard, the bigger issue was the trouble and expense of maintaining it. Simply put, they were cheap. And it is for this reason (more than any other) that it is unlikely that you will see either a new toilet or a better system for wag bag collection any time in the future.