One thing is that the majority of the truck fleet out there is < 10 years old.
I'm not sure about the trailers.
But, the machines do turn over relatively frequently. Change standards today, and in 10 or 20 years, most of the vehicles will be following those standards.
I can imagine more and more technology creeping into the cabs of the trucks. Some may not be popular with drivers, for example it would be easy to enforce the 55 MPH speed limit in some places. Drowsy driving detectors will come soon.