I have thought of one reason to not put the exhaust up front.
On my corvairs the exhaust, exiting at the back, will some times be pulled in by the cooling fan through the louvers on top of the read deck lid. The exhaust exit and louvers intake are close together. This means the exhaust will also be dispersed inside by the heater.
If the exhaust exited in front behind the rear wheel, the same could happen.
However, this happens so rarely I may still exit the exhaust behind the front wheel.
But if it happened even once, Ralph Nader would criticize the elio saying it was unsafe at any speed.