It should have been done after the trucks self-venting tanks proved to be efficient. I cannot tell you how many fires I have seen in the pit areas in the old days due to the gas over-venting and the catch can man not being able to catch it. It's safer, slower pit stops will be safer too.
Having worked the pits as a NASCAR photographer, I can tell you, on a mass pit stop, it is a war zone. I am all about safety in NASCAR, this goes along with safety barriers as being something needed for a long time.
Caz