Poly accomplishes two things, vapor barrier and air movement barrier. These 2 things can be (and probably already are to some degree) managed in other ways.
Vapor Barrier. A vapor barrier slows water vapor from pashing through it and the material it is in contact with (Like drywall). Some paints accomplish this.
Air movement Barrier. This is the more serious of the issues. An air movement barrier slows the air from moving around it, stopping the heat and vapor carriered in the air from getting around it. If you have drywall, you already have such a barrier.