Generations have always been ambiguous and poorly defined. If you look at how generations are usually divided and defined, you will not find any consistent rules in place in regards to how it is done.

Do you go by graphical improvements? Well if that's the case, you can't really consider the Wii a 7th gen console and the Wii U an 8th gen console. There is also technically a lost generation of consoles in the 80s consisting of the Atari 5200, Colecovision, and Vectrex.

Do you go by graphics AND features? Because the Nokia N-Gage and Tapwave Zodiac both technically introduced multimedia functionality and 3D graphics to portable devices, and in that sense ought to be 7th gen portables alongside the DS, Gizmondo and PSP. And yet they are considered 6th gen.

How about going by which consoles competed against the definitive systems of their gen? In that case, the Dreamcast would clearly be a 5th gen console, and Atari Jaguar, Amiga CD32, and 3D0 were all 4th gen.

Release year? How does one even determine a cut off "year" for a gen when all of these other elements are so poorly defined?

To me, the biggest example of generational weirdness is the placement of the SEGA SG1000. This is a system that is, in hardware, graphics, and controller design, literally a second gen console (early 80s second gen to be precise). It is LITERALLY a Colecovision clone, with virtually the same innards. It has a genuine third gen successor in the SEGA Master System. And yet...it is classied as third gen, seemingly only because it released the same day as the Nintendo Famicom.

Is the Switch 9th gen? It's hard to say, simply because we don't know what the 9th gen will be OUTSIDE of the Switch. Graphically, the system is certainly far away from whatever 9th gen would be. In terms of features, the Switch is currently pretty basic by even 8th gen standards, outside of its portability. In terms of release date, the system is literally launching between two 8th gen refreshes, and is unlikely to be competing against XB2 and PS5 any time soon.

As I see it, there are really only two solutions: consider what we are in now "Gen 8.5", or essentially accept that we are in the same generation, dealing with an industry-wide hardware refresh that is clearly something new, but not new enough to be considered a brand new gen. This is my personal stance: even the Switch is effectively just an improvement on the Wii U concept, even if it lacks the full back and forward compatibility that PS4 Pro and XboneX have. There's also some precedent for it: the consoles released in the early 80s were effectively a new gen with significantly better hardware then early second gen systems, killed prematurely by the American video game crash. Atari even released a 2600 successor, giving them two second gen consoles, ala Wii U and Switch.

The other solution? If the Switch is 9th gen, then so is PS4 and XboneX, and all three ought to restart from square one. Of course, from a market share perspective, this is impractical and paints an innacurate picture. Yes, Pro and X have forward compatibility, while Switch and Wii U do not. But forward compatibility itself isn't unheard of in video games: Game Boy's 5th gen successor, Game Boy Color, had a significant amount of forward compatibility with its predecessor. Given that Switch, Ps4Pro, and XboneX all have relatively moderate graphical boosts, and introduce new features their previous iterations did not have (portability & 4K gaming), and they are all coming out within a year of each other, they do tick a lot of boxes required for a new generation. I don't agree with this one, but I find it to be more consistent then "Switch is 9th gen" and less lazy then "generations are dead.

Addendum: regarding the "portability and 4K gaming" feature set of a hypothetical 9th gen, such a dynamic isn't dissimilar from motion gaming vs HD gaming from early 7th gen. One could argue that HD gaming was a critical feature of the 7th gen, yet the gen's victor didn't have it. So the XboneX and PS4Pro need be portable to have 9th gen features, and Switch need not have 4K. Both portability AND 4K are 9th gen features in their own right.

also your wrong about "successor = new generation".

We re talking about hardware here, not humans.

http://www.dictionary.com/browse/generation

1) the entire body of individuals born and living at about the same time (this is the one we use for consoles)

2) the term of years, roughly 30 among human beings, accepted as the average period between the birth of parents and the birth of their offspring.

3) a group of individuals, most of whom are the same approximate age, having similar ideas, problems, attitudes, etc.

1) & 3) are what we apply to hardware consoles... always has been.

We look at "gens" as a whole, gen this had x,y,z in it.

Just because Switch is a new console, doesnt mean its a new gen.

If it spends most of its lifetime with others from the 8th gen, then it belongs to the 8th gen.

Why does this always happend everytime theres a new thread about "gens".

^ this, what Ka-pi said.

Wii U + Switch both belong to the 8th generation of consoles.

Who care which arbitrary gen number a device has? All that matters is if they still get support.

3DS, Switch, Xbox One, PS4 and PS4 Pro are current gen: they all get a lot of new games, the hardware is still advertised and most software/network features still work

DS, Wii U, Xbox 360, PSP, PS3 and Ouya are legacy gens, where the support died or almost died.

I still count the Vita as "current gen" due to the remaining (third party) support, but it is on the verge of becoming "legacy gen" due to the lack of first party support + advertising and some cancelled features.

I base my logic on console generation using the history itself:
"Switch is 8 gen console because is competing with PS4 and X1".

X360 also did that with PS2 and also Dreamcast with N64 and PS1.

"Bu-but X360 and Dreamcast were more powerful than it's competitors!"

Arguing about power on a discussion about generations is beyond ridiculous, bc you are arguing against the whole definition of "generation".

Nintendo before always participate in a generation with a portable and a home console.

But now they started a new cycle with a whole new device. This pretty much confirmed the beginning of a new generation for me.

There's some overlap here as Generation Z overlaps in the years of Generation Y (Milennials).

But I'll just say it was a bad example. 

So lets take a look through History...

The NES is 3rd gen, sega master is 3rd gen. 

Sega's next console released only 3 years after the master and 2 years before the SNES. 

Basically sega released 2 consoles before nintendo released the NES's successor, YET it is still considered different generations. AND the genesis was discontinued at the same time as the NES even though it was in the same generation as the SNES. 

But because it was the successor to the master it's categorised as 4th gen. 

*Breathes out* 

Generation titles dont make any damn sense at all.

It used to be evident before, because every new gen, you could clearly see a drastic improvement from the last.

Its not like that anymore, we should stop useing "gens" monikers.

And at the same time portions of the music and movie market are buying records again in greater numbers and pushing for higher fidelity movies on physical media.

Having access to a movie only when a service has an agreement to stream it, and having 4K streams that look and sound worse than a 1080p bluray are not my thing. 

Yeah, because being able to play games like BOTW  or MK8 whenever and wherever it's not a huge improvement compared to previous gen.