Like as not, unless there is a serious turn in the materials science technology, probably the only people who will universally change to composite cases will be the military, where there is a significant weight savings issue, and not intention of reusing spent cases.
Now, just because the military does something, it is not automatic (NPI) that all production will convert over. Not unless there are considerable cost savings in the switch.
Enameled steel cases area "thing" because they meet military specs and are cheap for use in milsurp arms. Nobody is reloading those. The reloading industry is not a small thing, either, it's likely that the brass/gilding metal case industry will be around for a long time.
And the hunting round industry is pretty big biz, too.
Even if the military adopts a composite (polymer walled, gilding metal base) case for the 6.8, the ammo companies will not start making those cases for all the ammo lines right afterwards.