It'll (probably) fit as the Rev D is installed on the underside of the boomerang board and I can't imagine they put stuff extra stuff in there although I haven't seen the inside of an Elite controller.
I, and no one at the shop, knows if the software is compatible. If it does work, there's a good chance that our modchip won't understand if you remap buttons to some of the extra bits they added to the Elite. IE: if you were to change RT to the right top paddle and then try to activate rapidfire it probably wouldn't work, but we have no idea. Go nuts though! And let us know if it works!