Having said that, I do somehow feel you might be missing a really valuable learning experience here. And yes, this is only my personal opinion, but most photographers start out with really basic kit and then explore it until they have worked out the limitations for their needs. I'm not sure going with a full frame MkIII will give you this experience...
The culture of such thinking fascinates me. I sincerely mean no offense with what's to follow. It is not meant to direct at you but a general point to all. So here goes ...
What is the experience lost here? and how would that reflect differently with a Rebel class versus, oh let's just say, top-of-the-line 1D class?
You see, at the end of the day, any camera is simply a camera. That is they take pictures exactly the same way -- through a lens, shutter, and eventually the film/sensor. The ritual of acquiring a photo is also consistent -- point/compose, focus/meter, then shoot away. Yes, the 1D sensor, its magical AF system, its elaborate menus and options make a joke out of the Rebel, yet the fundamentals remain the same. Ya still gotta learn how to compose a great photo. Ya still gotta learn how to focus and hold steady. Ya still gotta learn how to expose optimally. Until there's a major breakthrough in picture taking, there's no learning to wield the extra stops of dynamic range or the ISO sensitivity per se.
"Careful you'll burn yourself if you use all 12 stops of DR!"
"You'll shoot your eye out if you turn up to 12fps too soon!"
Again I defer to my Ferrari analogy posted earlier.
Noob buys a 562hp Ferrari 458 as a 1st car. Ridiculous! The cost of inexperience is likely death. Too much power too little skills.
Noob buys a 1D as 1st camera. Wasteful perhaps. The cost of inexperience here is bad photos, which is just as likely with an inexpensive camera. No harm, no foul.