The PS4 uses a proprietary architecture.  They had AMD create a custom APU for them.  I don't know of any other device that has the same architecture as the PS4.  One x86-64 bit architecture is not always the same as another.  The XBox One is x86-64 bit, but PS4 games are not compatible with it, and vice versa.  You are not able to play PS4 games natively on your x64 PC.  

I highly doubt that the PS5 would just be an up-clocked version of the PS4.  Sony will most likely go back to the drawing board, and use the best technology possible to gain the most performance for the lowest price, even if they chose to use x86 components.  If the PS5 is just an up-clocked version of the PS4, everyone will just call it a PS4.5, and that won't win them any support.

If the architectures are similar enough, Sony could potentially emulate the PS4 on the PS5, so that games could take advantage of more memory / more cores / faster GPU / etc.  Going the other way is quite tricky though.  If the PS5 has some new feature (like a built-in PhysX engine), how would that game run on the PS4?  Would the dev want to build and test 2 different versions of each game?  Would Sony try to emulate this feature on the PS4?  In my opinion, the answer to both questions is no.  As consumers, we will demand that devs take advantage of all new features, otherwise we will label their releases as lazy ports, and sales would suffer.

people don't mind playing at 30fps now? now? NOW!?

http://www.gamepilgrimage.com/SATPSracers.htm

http://www.gamepilgrimage.com/SATPSRPG.htm

http://www.gamepilgrimage.com/SATPSFPS.htm

And it wasn't any differently with n64 games. 

https://www.youtube.com/watch?v=Snu7UipEIj4 (read video describtion)

This nagging about framerate and resolution is louder than ever and developers actually put more emphasis on this aspects.

Well, yes and no. The PS4 isn't a proprietary architecture. it's however a proprietary system. 

On a chip basis, it uses the same jaguar cores for the CPU that's in the XB1 and AMDs APU chips, its GPU uses the same GCN cores found in the southern islands AMD gpus. It uses GDDR memory, a sata 2 interface...etc. There is nothing proprietary about that. Every single thing mentioned can't only be improved but in most cases their next gen counterparts are already available. Hell even the OS is based on FreeBSD Linux. 

Whats proprietary about the PS4 are its APIs and shader language. So its the software compiler that differentiates it from PCs and everything else. 

Now with the PS5, the graphic cores can be better/more, but they will still be compatible with the GCN architecture found in the PS4 today (if you know what makes up a GCN core, then you'll understand why I say this). The CPU will have more transistors and be better all round, but they will still be an x86-64 CPU. All Sony has to do to ensure full cross compatibility, is just keep their current APIs and/or PSSL. So that way its even easier for devs to get into the new gen since all their existing tools will just work and all they have to do is make accommodations in their engine for the more powerful CPU/GPU and faster or more efficient I/O bus. 

The devs won't have to build two versions of anythjng. For them it will literllay be like making a game to come with High, medium/low settings. 

The x86 architecture on the PS4 will allow for an add-on that will let PS4 owners make the jump to PS5 without purchasing a PS5. This add-on will boost/replace the GPU/CPU/APU/whatever and allow players to run PS5 games at either lesser or equal specs. Conversely, this could also allows players to run native PS4 games at higher resolutions and FPS.

OR you could buy a PS5.