Considering the advances in polymers, I doubt it will be all that long before a reliable and durable barrel is made in some form of "plastic". Of course, it would be easy enough to avoid the issue for now with some form of sleeve, inside of the barrel.
This is almost deja vu all over again! (Thank you, Yogi Berra)
In the 1950s a company named Armalite built an automatic rifle called the AR10 with a thin steel barrel inside some kind of carbon-fiber like material.
In testing, it blew the end of the barrel out. So they went to all steel, and were asked to go for a cartridge called the 5.56 in the AR15 and, well, you know the rest of the story...