Off the top of my head 3.8mm is only about .145". Hardly a lot of material to start with. And then the wear limit is .80" ? SO we get all of .065" in material to play with. Ok. I hope when it's time for new rears there are 3rd party drums and shoes available to me for fair prices.
Aftermarket shoes are already available. I used Raybestos 1059PGs. Drums won't be necessary unless you do what I did and let your brakes go until they are metal-to-metal.