I am going to be a broken record here.
This would help in the promotion of having a new home built with a PWFS. PWFS cost around 1/2 of what it cost for a traditional foundation to be built and by design they are already prepped for Radon Mitigation. The only additional work or cost would be for a fan & vent pipes.
If a double sided slip joint (you may call it a vapor barrier) is not installed, then the PWFS is not built correctly.
PWFS are simple to build and cost less then traditional foundation systems but, you need to follow the engineering plan.