It seems like if you aren't racing, one could challenge themselves in many more pleasurable ways on a bike. Personally, I'd rather do a supported ride around Italy and end the day with a beautiful meal, a glass of wine, and a comfortable bed but that is me.
However, I have done a fair bit of long distance self contained touring as well, up to 8 weeks at a time, in various locales around the world, albeit with a proper touring bike which was fully loaded, like 90lbs/40kg (bike and gear). But never the 24 hour endurance type stuff that you're talking about here. I would agree that riding day after day like that does change your metabolism (unless you were doing that before), but despite what was just said, I will never agree that "it is very easy to ride 24hours straight on a bike", even for a good rider. There have been times when I've just been cruising along just zoning out, and have gotten so relaxed that I indeed, came very close to falling asleep on the bike. I pull over at those times and have a nap. Those days are long gone for me now, however. But some great memories remain.
But good for you if you take on the challenge... and if you do, I hope you document the entire trip and post up here so we can follow along and (sort of, but not really) feel your pain.