"Moving to a different CPU - even if it's possible to avoid impact to console cost and form factor - runs the very high risk of many existing titles not working properly," Cerny explains. "The origin of these problems is that code running on the new CPU runs code at very different timing from the old one, and that can expose bugs in the game that were never encountered before."

To me this is clear. Using ryzen cpu will break backwards compatibility. That's why I'm guessing ps5 will have 4 ryzen cpu cores + 8 jaguar cores if they go for BC.

My guess is that console games for ps4 are specifically designed to work with 6 jaguar cores. But this what Mark cerny said about this subject when talking about ps4 pro:

But surely x86 is a great leveller? Surely upgrading the CPU shouldn't make a difference - after all, it doesn't on PC. It simply makes things better, right? Sony doesn't agree in terms of a fixed platform console.

"Moving to a different CPU - even if it's possible to avoid impact to console cost and form factor - runs the very high risk of many existing titles not working properly," Cerny explains. "The origin of these problems is that code running on the new CPU runs code at very different timing from the old one, and that can expose bugs in the game that were never encountered before."

To me this is clear. Using ryzen cpu will break backwards compatibility. That's why I'm guessing ps5 will have 4 ryzen cpu cores + 8 jaguar cores if they go for BC.

Cerny is right on the money there. Game engines on consoles sometimes have a "tick rate" that is tied to the clock rate/performance of the CPU.

It's an extremely rare occurrence... And I would be surprised if any modern game/game engine even takes that approach in the modern era anymore... Besides, such issues would have become apparent on these mid-generation consoles refreshes anyway.

And... Disagree with you here.

From a hardware feature set point of view, Ryzen should be fully backwards compatible with Jaguar from an ISA standpoint, so the real caveat is entirely performance based.
CPU's these days have a varying degrees of clock-rates that they can operate at to meet various performance/power targets.
There are dozens of ways you can influence that to meet backwards compatibility goals, possibly even use the power of abstraction.

Next-Gen is highly unlikely to use Ryzen CPU cores, well... Not the Ryzen we have today anyway.

This says nothing without deeper knowledge of how the majority of games for the console are programmed. It might be solvable with a simple patch and if it's connected to clock speeds it should be easy to have older games run in a legacy mode where the PS5 just locks it at lower speeds.

The tools that are used to program for PS4 should be old and standardized enough to make any software issue solvable without resorting to legacy hardware. I don't really think it's possible to program a game so statically that a newer processor can actually break it. Especially considering that the vast majority of games runs on multiple platforms and as such shouldn't be hardcoded to specific hardware platforms.

My guess is that console games for ps4 are specifically designed to work with 6 jaguar cores. But this what Mark cerny said about this subject when talking about ps4 pro:

But surely x86 is a great leveller? Surely upgrading the CPU shouldn't make a difference - after all, it doesn't on PC. It simply makes things better, right? Sony doesn't agree in terms of a fixed platform console.

"Moving to a different CPU - even if it's possible to avoid impact to console cost and form factor - runs the very high risk of many existing titles not working properly," Cerny explains. "The origin of these problems is that code running on the new CPU runs code at very different timing from the old one, and that can expose bugs in the game that were never encountered before."

To me this is clear. Using ryzen cpu will break backwards compatibility. That's why I'm guessing ps5 will have 4 ryzen cpu cores + 8 jaguar cores if they go for BC.

This discussion is getting slightly out of my wheelhouse. But what Cerny was referring to had nothing to do with clock rate or clock speed. What he meant was that newer cpu architecture run game codes at different timings than old ones. This is way for cpus to increase ipc (performance per ghz). But because game code running a bit differently on newer cpu architecture this can cause bugs when running ps4 games. 

This is why Cerny says this can make many titles not working properly and not "an extremely rare occurence" as you put it Pemalite.

But again this is a little above my knowledge. So I'm probably about 90% right here.

Meh, let's turn that down to 10%. I am not as knowledgeable as Pema is in these things but I'm quite confident in my basic logic.

All games use the same base instruction set on the same base architecture called x86. Notice how the article starts with the words "backwards-compatible". It's basically built for that sort of thing. Between platforms there doesn't have to be any kind of conversion, the CPU will read the code as is and will execute it. They're generally extremely flexible too and can adjust on the fly. So if you worry about any timings that are somehow unique to Jaguar and have nothing to do with the clock for some reason, that too can be fixed by adjustments on the fly.

We're talking about software issues here and they can all be fixed by software tweaks since the architecture itself is compatible with each other. No developer will completely hard code everything specifically for a single narrow piece of hardware. Especially not multi platform games, so you can scratch all of those already as done.

Your worries already invalidate themselves at the base logic of programming.

This is why Cerny says this can make many titles not working properly and not "an extremely rare occurence" as you put it Pemalite.

But again this is a little above my knowledge. So I'm probably about 90% right here.

This discussion is getting slightly out of my wheelhouse. But what Cerny was referring to had nothing to do with clock rate or clock speed. What he meant was that newer cpu architecture run game codes at different timings than old ones. This is way for cpus to increase ipc (performance per ghz). But because game code running a bit differently on newer cpu architecture this can cause bugs when running ps4 games.

This discussion is getting slightly out of my wheelhouse. But what Cerny was referring to had nothing to do with clock rate or clock speed. What he meant was that newer cpu architecture run game codes at different timings than old ones. This is way for cpus to increase ipc (performance per ghz). But because game code running a bit differently on newer cpu architecture this can cause bugs when running ps4 games. 

This is why Cerny says this can make many titles not working properly and not "an extremely rare occurence" as you put it Pemalite.

But again this is a little above my knowledge. So I'm probably about 90% right here.

Pemalite said: 

If you can find evidence that points it to being a common occurrence where taking a game from the base Xbox One/Playstation 4 and running it un-patched on the Xbox One X/Playstation 4 Pro introduces timing bugs and so on, then I will retract my statement, because as far as I know... It hasn't happened. Ergo. Not a common occurrence.

Games generally don't tie their tick-rate (The heart-beat a game operates at that everything runs in sync with) to clock rate anymore.
It was stupidly common on the PC back in the DOS days, which is why old-school PC's had a turbo button, so that the PC would operate at a faster and lower clock to keep things that tied their tick rate to clock speed in sync.