The problem with that is heat. The engine generates a lot of heat under the hood. What the stock airbox does is take air from a cold source, usually the front and then protects te air from the heat of the engine. Engines prefer colder air, however the stock airbox is usually restrictive. Which is why people switch to a less restrictive intake. The idea of a Cold Air Intake (CAI) is it works in the same way to draw cold air in, usually from down low in the bumper and makes te path the air travels less restrictive allowing for gains in performance.
The best aftermarket intakes (Dinan, Conforti, etc) either put the filter down low in te bumper area (more so E36) or have a heat shield to keep the hot air away.
In this picture is my Jim Conforti CAI on my E36. You can see how the heat shield creates a barrier when the hood is closed.