Upload & Sell: Off
Because people buy a camera upgrade / line expecting the same form-factor. Everything from lens balance to working with the camera in the dark remains the same. Makes switching bodies on the fly easier.
If you want a new factor, you buy another line. Unfortunately, you can't throw everything and the kitchen sink in with every factor (well you COULD), but that's not how marketing works
No you're thinking of the design of a tool. What I'm talking about is design of a consumer item. Because honestly, this camera is somewhere between the two. I think Canon envisions the rebel line as 'consumer', XXD line as 'prosumer', and the other lines like the 7D, 5D, or 1D as being 'pro'.
Think of something like the car. Sure it has a purpose, a function. But it is also a consumer item. Because of this, every few model years, a specific model of car is re-designed. They have to do this, if for no other reason, to keep it fresh, to keep it appealing to the modern consumer.
You don't see it much on these boards, but these boards represent an ever-shrinking portion of the photographer population as time goes on. It's not so much that the number of users on these boards has been shrinking, but more that the users of these boards are only a certain type of photographer that continues to be eclipsed by other types as time goes on.
Imagine, for instance, if this new camera was sold for the exact same price as the SL-1. Which camera do you think Canon would sell more of? It might seem like a stupid question, but it should be illustrative of my sentiment, at least.