This particular battery configuration was actually quite common back in the day with cheap, plastic incandescent lights. A classic example was the old plastic Duracell Durabeam from the 80s. But I have not seen it with newer LED lights.
Plastic is fine put the emitter on copper and make the business end metal. it doesn't have to be the brightest thing in the world either.. I'd take a nice nichia ,a nifty driver and maybe another emitter like the swm light too.I suppose it could run on two 14500's as well... How about an electronic clicky 3 mode ramping easily presettable light while we're at it ..