If it's only $400, then it's definitely not going to be a 4K gaming machine.

Maybe Sony, is taking losses to sell it for 400US$

Yeah a loss of 100%. I't won't be a 4K gaming console. I still don't understand how anyone thinks it will be. More likely a Slim model with 4K video streaming, and possibly slightly more optimized. 4K just doesn't make sense right now, majority don't even own 4K tvs and the currently model of PSVR couldn't even take advantage of 4K. 

I dont think there will be another PS4 after the PS4.5.

I think the plan from here on out is to do half steps.

4.0 -> 4,5 -> 5.0 -> 5.5 ect

^ this.

The 4.5 is just a normal slim.. but because the step from 28nm -> 14nm FinFETs is so big... not only can they shrink it and make it less power hungry, but they can do that and make it faster at the same time.

Its just a slim version that upscales things abit.

I wonder how many clicks these sort of rumors have generated...... It's amazing that so many actually believe that sony would make a PS4.5 or a PS4K.

While I agree it would be a huge loss, I suggest you look at your numbers again. 100% loss would giving it away for free. 

There is some sense to it. AMD Zen already have been previewed to have 4 to 10 cores, 14nm and 30% increase in IPC over Godavari. This should put Zen to the level of Skylake in IPC. Polaris is a whole new architecture, not just a 14nm refresh of current GCN.

Zen is also supposed to support HBM as a primary memory which would allow HBM to be the total memory and the CPU shared memory.

So yeah, I expect the Zen APU to be at least 30% faster clock-by-clock than current Steamroller APU's, and they're already 10% faster than Jaguar's, whilst keeping power-consumption and heat to a minimum.

IMHO:
Sony will almost definitely release a slim PS4, if they name it PS4K or whatever, good, I don't care about naming and most people don't too. If the PS4.5 is just a refresh 14nm, better looking, cooler, with more HDD space, awesome. Bring it on. This DO NOT appear to be the case.

However pretty this sounds, there are a couple of mistakes here.

1) It's not that easy to upscale graphics. Upscaling images is one thing, another totally different is to upscale heavy graphics. Example: Buy a GTX970 and game at 4K. You can upscale it right in the control panel. The GPU takes a serious hit in performance. It's lighter than gaming at actual 4K, but it's definitely NOT performance-hit-free.

2) If it's a brand new console, not just a refresh with new name, then it will absolutely NOT have 100% compatibility with PS4. It's a totally new architecture, it's a totally new design, the IS is totally new, this will absolutely be a headache for developers. If a game is release for the PS4 it will need a compatibility patch for the PS4.5 and vice-versa. Not only that, but it's phisically impossible to run a game equally in both machines.

3) Games are heavily optimized softwares, a game with compatilibity patch will not run well in a environment it was not supposed to work on. If however they program two different executables from the same source, the game can run fine, but another compile is going to take a major space. Not impossible, but definitely another headache for developers.

4) Studios are almost always profit-oriented and will not make a game for two similar platforms for the same company. The contract itself will be different for every SDK. If Sony makes a global contract and a global SDK, studios may be able to focus in both consoles, but quality is not guaranteed. Otherwise studios will only focus in one platform, making the other platform a rotten apple and eventually killing it.

5) This opens a great window of opportunity for M$. They're already behind this generation so why waste effort on it? They can shift the focus entirely to the next-gen and release a superb console in 2 years. Sony will not release the PS5 in 2 years(from the release of PS4.5) and make the fan base utterly upset. Microsoft will have a loner game against itself it they play their cards right, while Sony still lingers from PS4/4.5 success. If Sony decides to compete with a PS5 in 2 years, then the PS4.5 will be a waste and they will kill it shortly, making a waste of money and R&D.

TL;DR
It's plausible for Sony to make this console, it's possible for it to output 4K(although the PS4 is already capable of that, just read your goddamn manual!), it can game better than PS4. It won't be totally compatible with the PS4 if it's a totally new system(otherwise it will, if it's just a refresh), and it will most likely kill a PS5 plans in the making for at least 4 years.

Not liking the Idea of this 4.5 at all. Only had my ps4 less than a year now. I hope the NX is on par and gets alot of the same games now.

Hopefully they are right. A new PS4 that is capable of 1440P upscaled to 4K would be a perfect fit for new comers, and those looking to take advantage of their new 4K TV's.

Also, if this new model added a couple more USB 3.0 ports in the back, the additional HDMI port for PSVR, and the rest of the PSVR chip set, it could eliminate the need for the PSVR sub processor box. This would be a quick way to cut the cost of the PSVR in the near future, for Sony and consumers.

It dosn't end there though. If this new PS4 is truly a bit more powerful, then it could be a huge benifit to those who pick it up for VR. Although it won't put out 4K due to PSVR only having a 1080p screen, it will help accelerate the frame rate, and in VR frame rate is extreamly important.

These upgrades during the life cycle of each generation are a great direction for the industry, and I am very glad to see all three console makers moving to this approach. We are at a point where tech is not growing fast enough to justify a new generation every 6 or even 10 years. However, it is progressing just enough to make giving consumers options for slight performance increases throught the life cycle a very desirable business model.

As others have said, this may only be the first upgrade PS4 gets throughout its life. We could possibly see another upgrade around 2019 or 2020. Like I said above, the tech is just not advancing fast enough to make actual generational leaps in the tradition console cycle, so these performance tiers are a nessesity. I don't expect to see a true PS5 on a radically new architecture until at least 2024, because, CPU, GPU, RAM, and SSD tech will not be advanced enough for a full leap to 4K until then. At that point 4K VR will be the norm and 8K TV's will be starting to ramp up.

2024? By that time, a smartwatch will be more powerful then the current PS4.

My guess is that the next generation of consoles will be in late 2018 or early 2019 when Nvidia Volta/Next-Gen AMD arhictecture releases.

Of course if console gaming still exist in the future, with mobile gaming and PC gaming taking over...