This sounds a nice idea. I always thought escape was a bit too far to press.
I won't use it for two reasons. Firstly I've used up Caps Lock for a much better purpose, see my reply to this poll. Secondly, I don't use vi*, so I use escape much less frequently during editing and those times it's always a modifier, so I can just use the Alt key (either of them, I don't make this riddiculous distinction between Green Alt and Alt Gr). Other then these, I agree with your idea.
Finally let me note that a friend of mine uses vim and has remapped the two-character sequence ;x to escape in it, as it almost never appears in text and is easy to type. That has the advantage over your method that he doesn't have to install any special software to change the keyboard settings, as the mapping is done by vim itself. Also this way he doesn't have to find out how to do the remapping on every system separately (like X, Linux console, OS X, Windows etc). I had to experiment much to make the same sane keyboard settings work both on the Linux console and X.
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