It's hard to even say if they'll both do it the same way anymore. The short answer for the OP though is that I think there's going to be optional forwards compatibility. Developers will be able to keep supporting PS4 and Xbox One but won't be forced to.
With Microsoft, it's possible they may reach a point where they stop mandating support for the original Xbox One, and Xbox One X becomes the minimum spec. If that happens though, it's not like developers will immediately stop supporting original Xbox One for a little while. Many will likely keep making their Xbox games run on it, like EA Sports games or COD or other mass-market AAA games. You'll just see other games start to pop up that are Xbox One X-only.
It seems Sony is going to stick with "generations" but just like Microsoft, there's no reason for it to drastically change the architecture of the PS5. It'll just be the same system with more memory, a better GPU, and a new CPU, the CPU being the only thing that might cause compatibility problems.
Right now what I think Sony is going to do is launch a PS5 some time around 2019 or 2020, with backwards compatibility and optional forwards compatibility. A bunch of developers like EA and Ubisoft and the like will make games that are basically PS4 games but might run in an enhanced mode on PS5, while others like Sony will make PS5-only games. It'll basically be the same as cross-gen games but as one SKU. Maybe they'll label them "PS4 and PS5" on the box.
No. I think when the "NextBox" comes out you'll just keep playing the same Minecraft you bought on Xbox One, but it'll receive another "Super Duper Graphics" patch to take advantage of that new hardware when you upgrade. I think that will happen for lots of "live games" if they're still popular when the next round of hardware gets here. Stuff like Destiny 2 and Red Dead 2 might get PS5 patches.
With Microsoft, it's possible they may reach a point where they stop mandating support for the original Xbox One, and Xbox One X becomes the minimum spec. If that happens though, it's not like developers will immediately stop supporting original Xbox One for a little while. Many will likely keep making their Xbox games run on it, like EA Sports games or COD or other mass-market AAA games. You'll just see other games start to pop up that are Xbox One X-only.
It seems Sony is going to stick with "generations" but just like Microsoft, there's no reason for it to drastically change the architecture of the PS5. It'll just be the same system with more memory, a better GPU, and a new CPU, the CPU being the only thing that might cause compatibility problems.
Right now what I think Sony is going to do is launch a PS5 some time around 2019 or 2020, with backwards compatibility and optional forwards compatibility. A bunch of developers like EA and Ubisoft and the like will make games that are basically PS4 games but might run in an enhanced mode on PS5, while others like Sony will make PS5-only games. It'll basically be the same as cross-gen games but as one SKU. Maybe they'll label them "PS4 and PS5" on the box.
It will be interesting to see what happens to the GAAS games. Like will Minecraft get a nextbox version? Or will the Xbox One version be pushed? If it gets a nextbox version what convinces me to buy it again when my Xbox One version works with everything?
No. I think when the "NextBox" comes out you'll just keep playing the same Minecraft you bought on Xbox One, but it'll receive another "Super Duper Graphics" patch to take advantage of that new hardware when you upgrade. I think that will happen for lots of "live games" if they're still popular when the next round of hardware gets here. Stuff like Destiny 2 and Red Dead 2 might get PS5 patches.