6.8 has grown enough to market 6.8 specific bullets with ogives matched for it's use. We're not stuck using a long case .270 any more.
If bullet makers are willing to spend money to offer 6.8 specific bullets, I would hardly call the caliber dead. If anything, they are selling out regularly, and the market is demanding more.
Consider that five years ago, the list was pretty much 6.8 Remington, and now, count up what's out there. That many makers with that many offerings? Not hardly dead, and likely around for decades to come.
How old are the .30-06 wildcats? 60 years and counting, still on the shelves.