Perhaps you are correct as new cartridges are being brought out all the time. I see Hornady has a new .375 in the wings which looks pretty good. By the time 10 years has passed, even if Remington decides to discontinue the .375 Ultra, it is unlikely that the other cartridges based on this case will also dropped - therefore a brass supply will continue to exist for quite some time. After all, we can still buy brass for the .348 Winchestrer and the .350 Remington.