LOL - by that theory Wii U is generationless because I can play NES SNES N64 Gamecube Wii gameson it
LOL at you, you just have to read. He gave a good definition that works for your example. The Wii U play NES games, but the NES don't play Wii U games, not to mention incompatibility for accessories, so they are different generations.
Anyway, it could be the end of the generations as we know them, but in this case just like the PC, it will rise some questions about compatibility. I can't imagine developpers keeping full compatibility with hardware more than 10 years old. Which means compatibility between PS4 and PS4.5 would be lost at some point.