Hey, you just described my day job! So let me respond in a little more detail. The watchwords in this kind of analysis are "meaningful" and "precision." Are you familiar with the coastline paradox? The closer and closer you look at this problem the less meaningful the information becomes. Once you subdivide and carve established brackets beyond what researchers are actively observing, the unity dissolves to an infinite fractal and it is no longer significant, much less useful.

Instead of shifting into ever more thinly sliced demographic cohorts, things like microtargeting rely instead on psychographics (broadly, social behaviour beyond a/s/l) which are proving to be much better predictors of behavior in fields such as marketing and behavioral economics.

For several decades the 15-20 year "generation" has served as about the most precise grouping that still provides useful information. The field hasn't stopped there, but it has shifted how we think about grouping people. "Xennials" is up there with "ambivert" and MBTI profiles in pop-sociology as expressive identity in a field that doesn't need any help undermining its own validity. :/