If every game released is playable on the original PS4 model, I don't see how it will add any length at all. Games are still going to start to stale and devs are still going to want better machines because they're going to have to keep dumbing them down.

It's not devs that decide when a new generation is in order, it's when the sales curve starts going downwards. With a new model and lack of cheaper slim model the peak will be reached later, lengthening the generation.
Duming down has nothing to do with how long a gen is, sequelites setting in is a valid concern though.

Pure conjecture. There's no evidence of a mass exodus of console gamers towards PC or just away from consoles in general.

Those are Houses and Spencers words, thats what they are aiming at, so the strategy for releasing this thing, acording to the ppl who developed it, is stoping PC exodus and also stop ppl from loosing interest overall later on the generation.

Yes we have. It's not common with consoles (the last notable spec update for a console was the SG-1000 being upgraded to the Sega Mark-III/Master System), but it's regular with handhelds (see the GBC, DSi, and New 3DS). The effects were comparable to slimlines & price cuts.

You are comparing apples and oranges. Handhelds and consoles are 2 completly different beasts and the New3DS is hardly comparable to what these consoles upgrades are suposed to be. We have 0 info about how this will play as it never happened before.

Evidence suggests the U.S. market actually maxed out in the sixth generation and has remained flat. The Wii overinflated last generation. It was not a conventional console, it sold mainly on the merits of its low price, good gimmick, and good marketing, plus sufficient software to bolster the rest of that. But it did not displace 360 or PS3 sales, but rather complemented them. Had it sold as well as the GameCube while the 360 & PS3 still sold what they did, we would have seen fewer than 82 million consoles sold in the U.S. last generation, vs 77 million sixth-gen consoles. The Wii U's commercial failure is already resulting in combined console sales across all three major brands to experience a huge drop gen-over-gen, even though conventional console sales remain healthy. Combined PS3 & 360 sales in the U.S. were 69.6M vs. 61.4M for combined PS2 + Xbox sales, a decent increase, but don't forget the Xbox was discontinued and replaced prematurely for reasons outside MS's control, so it should have sold more than it did. If the market is still increasing, it is a function of population growth more than anything else. Also, there is the unaccounted for variable of multi-console households.

The reasons why the market might be growig is beside the point, if it is because population is now 100 times biger or because the same person is buying 30 consoles Sony and MS do not care. Nintendo lost a lot of its market, Sony and MS didn't. They gained a bunch of ppl who were with Nint.  If the Wii had sold as much as the Gamecube itd've been a failure kinda like the WiiU is, fact of the matter is the Wii did not sell as much as the Gamecub and at least a small percentage of the ppl who bought Wiis and were not realy into videogames before certainly became fans/ were introducted to this world after the Wii. Even if the market does shrink the simple fact that the PS4 is a very dominant cosole justifies its fast sale without compromising its capacity to have a deceantly long tail. Of course eventualy the sales will decline, it happens to anything, but you can't just predict it will decline on this year here because last gen had X consoles sold. And these mid gen consoles will make actualy knowing the size of the amrket rather impossible by the end of the gen since a bunch of ppl who already own a PS4 or a XOne will buy a Neo or a Scorpio and show twice on the tables even after selling their second hand PS4/One.

Mid-gen upgrades will not be the new norm. They will not do anything unprecedented. But I have a feeling that many people simply want things to get a shake-up. The end of console generations as we know will be something new and fresh, and on pure novelty alone is enough to get a few people interested regardless of whether it makes sense from a business or consumer perspective. But the mass market isn't ready for it, and there are very good reasons why the console cycle as we know it exists in the first place. There is absolutely no reason to assume an impending paradigm shift in the console market. The most reasonable assumption is that the status quo will be maintained and things will continue normally, with "proper" ninth-gen consoles being released within the next 4-5 years.

Ye I'm sure Sony and MS are releasing these upgrades, investing on marketing and develepment randomly, its not like they have a plan and believe they can suceed in it and profit from it. The most reasonable assumption is we haven't even seen the launch of one of these upgraded consoles yet, any asumption now is not reasonable, at all.