I think we might have a communication issue: if you are really running fat bike tires at 25-30 psi, you have got them inflated 2x (or more) higher than most people would run on the smoothest pavement.
Or are you actually referring to wider tires on mountain bikes?
Anyway, interesting idea on the rubber liner. I suppose the liner, along with the tire itself, creates a thick enough barrier that the goatheads can't penetrate through to the tube. Are you finding thorns stuck in the tires when people bring back the bikes?