There have been a few front engine Class A's in the past - I believe it was Spartan that had a "puller" chassis around 1990 and Newmar built some Kountry Stars on it.
There currently are some Class A variants like the big Dynamax Corp
Class A's and the Kibbi Renegade. And there are motorhomes like the Gulfstream Endura diesel on a Kodiak chassis which is called a "C" but can be up to 37 feet with three slides and plenty of basement storage..
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL