The generations have become muddled, and it depends entirely on whether you feel they should be separated by power or date.
In the first case, I think the Wii U more accurately reflects the seventh gen, with the Wii also fitting better in the 6th. Meanwhile, the PS4/Xbox1/Neo/Xbox upgrade/and NX all look like they'd fit comfortably within the 8th.
If it's dates... honestly I don't know, maybe we need to just acknowledge that there's a generation 8 and generation 8.5 this time around, and if that's the case then we can keep the Wii U in 8 as well. It would certainly keep things neat and tidy for the future.
It's not like we haven't had weaker consoles in the same gen as stronger in the past. The NeoGeo, for instance, towered over the Genesis/Snes etc, but it got lumped into the 4th gen right along with them.
If I had to vote on the easiest solution, it would be this:
Gen 8
-Wii U
-Ps4
-Xbox1
Gen 8.5
-PS4 Neo
-Xbox upgrade
-Nx
Really, the release of these upgrades for the PS4 and Xbox1 will actually kind of clean things up for us a bit in terms of grouping them. I sincerely doubt NX will warrant being considered a gen 9 console.







