I see on the xbox one Microsoft need permission from a dev to make a game BC. Will it be the same on say the ps5 for ps4 games? Or can Sony off the bat just make the ps5 fully ps4 BC and have the entire library work or can devs stop them? I ask this because I'm sure devs like R* want to release a separate version of GTA V to sell again. But will we see a situation where your ps4 version works and can he downloaded and in addition a ps5 enhanced version from R* sold separately?? 

You can make hardware completely Backwards compatible and not ask a single developer. When Nintendo made the Wii it was completely backward compatible with the Gamecube. You can play any Gamecube game on the Wii. Sony also did this with the PS2 as it was able to play PS1 games no problem. Developers can't legally stop the Xbox 4 and PS5 from being backward compatible like the Wii. However, Developers can pressure Sony and Microsoft to not do it by support means. Which means that they will treat the system with no backward compatibility with better support.

Honestly making a system backward compatible is a lot of work. You have to basically make two consoles in one. Which is why a lot of systems don't do it. Microsoft only has to ask developers to add a game to BC because digital rights are different from physical rights.

Thanks for the reply. I think ps5 will absolutely have BC because they don't want to give MS a selling point over them. Does digital BC work the same as physical? As in Sony don't need to ask devs to allow us to play our digital ps4 games on ps5? 

I know it took lots of effort in the past but if ps5 runs the same x86 architecture as the ps4 won't it be quite easy? 

I don't see why they can't if the tech isn't very different. The Wii wasn't that different from the GC, so it made it possible for BC. With there not being any weird tech like the cell processor in the PS3 (as far as I know), if the tech is not too different it could be possible for the PS5 to be BC I suppose.

I agree with you I'm just wondering on the legal side of things is there anything devs can do to prevent their game being available on BC. 

This is the 1st time I'm ever hearing about this. I've not known this ever being the case with any system with BC.

Can they, yes. Will they, Microsoft more likely than not, Sony maybe, and for shits and giggles Nintendo probably. All 3 console makers are probably going to simply use upgraded versions of their current architectures as opposed to older consoles where tech could be drastically different between generations. From a technical point there's probably nothing stopping backwards compatibility just like when you upgrade from a launch PS4 to the pro but whether or not everyone is consumer friendly enough to do it is a different question

They will probably go back to selectively allowing BC. A company like Take Two would sure love to re-release GTA V, Red Dead 2, and Borderlands Handsome Collection (even Outerworlds since they also own that if it comes out this generation). Without BC getting in the way of their plans, If all 3 hardware publishers decided to say that is final, then the devs and publishers will have no choice but to submit. If either one came out alone making every BC just like that, it would be bad for them and their relations with 3rd party.
Even if everything won't be 100% backwards compatible, we can trust Microsoft to deliver a very strong lineup of BC games next gen as they have this gen. More so people won't have any trouble dropping their old Xbox in favor of the new Xbox since most of their favorite games will still be playable on the system along with all the new titles for years to come.
I feel like BC is going to be a very important thing for the first few year of the next generation due to the games as a service model being a big thing.

I'm really interested to see what games will be made BC or re released due to their GaaS model. What will happen with Sea of Thieves, Or Rainbow Six Siege? Will they be re-released, or made fully backwards compatible with graphical enhancements. R6 is on year 4 and shows no sign of slowing down, and Sea of Thieves supposedly has a "10 year life span".

For phisical, not a problem.
For DIGITAL though.... If they want to do that they need to make a ps3 mode similar to how the Wii U has a Wii mode and 3ds has DS mode. Otherwise devs would need to approve.

Whether or not you'll be able to access your old downloads is an interesting question. Which seems to only be a problem for consoles. I mean when you consider other devices with stores let you access your digital purchases regardless if you change devices. I mean your move purchases can work on countless platforms and I can still access Android apps from like a decade ago.

I think we'll just have to wait and see. Has MS and Sony tweaked their deals to keep to allow people to keep accessing their downloads on future platforms? Does playing the games natively versus emulation make a difference? These are questions we won't know until talk about the 9th gen begins but I'm assuming we'll get the best case scenario, we can simply access our 8th gen purchases and play them natively on new specs.