Rendering at 4K doesn't take more work than rendering at 720p/900p/1080p.
Creating more detailed assets takes more work, but then that never stopped devs prioritizing PS3/360 over Wii and PS4/Xbone over Wii U/Switch.
Third party's main focus next gen will be on Playstation and Xbox, just like it has been for the past almost two decades. Switch won't impact PS5 just like it's not currently impacting PS4.
Well I just meant that no one will be putting out games with assets intended for 720p display on machines rendering in 4k, they would just look garish compared to real 4k offerings.
Say with things like the megadrive collection of games, those are coming from a 240p system and now being rendered at 1080p on current gen machines but hd alone doesn't make the game look nice, art departments will need to fully flesh out models and textures which will look at home in 4k.
You're right though that some AAA titles are going to be prio to the ps system and then due to similarities after you've made a ps5 game there's not much reason not to look at creating a port for the neXtBox
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