Our 2000 Residency built on the Ford chassis has served us well for the past 17 years so for me, I'm pleased with my "ford only" engine option.
Being manufacturers of diesel powered chassis I would think it would be highly unlikely that Spartan or Freightliner would venture into building gas engine powered chassis,and even if they did what gas engine options are currently available on the market to power those chassis.
Nice idea however and no doubt there would be benefits to have more than one engine option for a gas powered chassis.
Best regards and Safe Travels
Jim & Sherry Seward
Las Vegas, NV
2000 Residency 3790 V-10 w/tags & Banks System
2003 Suzuki XL/7 toad