There have been a couple of attempts at one but they didn't catch on. The Workhorse UFO seemed like it should have been a winner, but low-end front diesels like the Freightliner FRED kind of trumped it. Strange thing is, the FRED also died off due to lack of customer interest. RV manufacturers couldn't sell enough of them to justify an alternate chassis choice.
Rear engine chassis are more expensive to build, so maybe the price premium (vs a front gas engine) is more than the perceived value? Diesel pushers aren't just diesels - they incorporate air suspension and brakes, higher GVWRs and raised rail designs to give lots of extra value. A gas pusher with spring suspension and straight rail design looks like a poor cousin from the country in comparison.
The fact is many (most?) people purchase a coach based on the bling they can see and the price. Chassis options just aren't a big come-on.
2004 American Tradition; 2014 Buick LaCRosse
Homebase in the Ocala Nat'l Forest near Ocala, FL