With the amout of replacement components available, how often do you need to buy the same bike over and over?
People have been saying 26" is dead for years now but there are still a million flames out there, a plethora of components, and if one wanted a new bike one could just get a frame builder to make it, which is pretty easy these days.
Same will apply to 27.5 for decades I presume.
The only dead aspect is that you may not be able to read the ad copy in next years consumer oriented magazines that try to convince readers they need that years hot thing.
...so dead only really applies to the notion of consumer bait lust candy.