Unfortunately, there are many aircraft (including the Boeing 737)that have unusable rear slides when only the nose wheel is up or collapses. This is a particular problem for the 737 Freighter (it can carry freight forward of the passengers). I assume the designers expected a wheels down or wheels up situation. If the nose wheel is up and the main gear is down, the only available exit is the overwing one, which is now on a steeply tilting wing. Makes it hard to get the little old ladies off in a hurry. Made worse when the passengers don't all speak one language. And some of them don't have a word for nosewheel in their language.

Respectfully,

Jerry