Never mind all your motivation, there are at least a couple of issues that bear mentioning. They may be more or less important depending on season and timing but be sure you’ll have to face at least some snow and water. Hiking on either is nothing like hiking on dirt.
There was still lots of it in the High Sierra when I arrived in early to mid June during my 2006 thru-hike. The most popular concern about snow is usually the progression on steep, hard-packed snowfields with the potential for a slip and eventual fall that may be fatal. You need to be cautious about this, assess the risks and try to avoid dangerous scenarios as much as you need to know what to do if you do slip and fall. Nevertheless, I want to mention two other factors about snow that are not so much talked about, less technical but just as important: route finding and exhaustion.
These are both well known issues for the average backpacker as they’re relevant anywhere but they come to a whole new level when hiking on snow for extended periods.
In 2006, the trail was buried for miles. We spent as much as 30 hours straight with barely a hint of where the trail was. Bottom line: you need to be able to navigate.
In the high country, navigation is usually easy, weather permitting, by major landmarks but you still need to be able to read a map and find your way around. Be aware it’s you, the map and the landscape. Be proficient with this and, if you aren’t, team up with somebody who is (and take the chance to practice and learn).
Navigation is most difficult when snow is found in lower areas below tree line where landmarks are hidden by the trees and the terrain. Hopefully, this shouldn’t be an issue in a normal snow year but beware the exception and take special care.
Exhaustion is the less popular of the big issues. Hiking on snow can be exceptionally energy consuming, particularly when the snow is deep and soft so you sink. But also being on the snow for days, many hours every day, is itself a big energy sink. The snow is cold and, quite often, wet and no matter how warm it may get during the day once the sun is out cold temperatures set in. All this adds up and you need plenty of calories to keep your body working. I think you basically need to be aware the framework is different from what you were used to: you’ll be working harder and for longer hours to cover two thirds, maybe half the distance you were used to. Be aware of this and plan accordingly.
Hiking on water is even more difficult than hiking on snow. We sink in the water all the time. And water moves; sometimes, very fast. Fortunately, and by its own nature, water is not found all over the place for miles on end but that tiny stretch may be enough to be a problem.
I personally found the river crossings to be the most difficult, challenging and daunting thing I had to do in the whole trip. I’d even say it was the only really dangerous thing: not the snow, the desert heat, the rattlesnakes, the bears or Sasquatch but the river crossings.