It will take a little history to determine what they will be called. We can't determine it yet. The Genesis, for example, competed in the beginning with NES but later with SNES and history eventually grouped it with the latter. But for several years it was billed as a superior alternative to 8-bit tech.
We may see this with NX. If it's a hit with a long life, it may compete for a couple years with PS4 and later with PS5 and history will call it the first 9th gen system. If Neo has a short run, it could be remembered as a 8th gen update, like the 32X.
In another scenario, we could be witnessing the first ever half-gen, and the term "gen 8.5" may gain acceptance. If NX, Neo and One Point Five all launch and have decent impact and life span of 4 or 5 years, commentors may feel the half gen was its own piece of history.
Time, lifespan and success will likely determine the labels.
