Sony has confirmed that while Ratchet and Clank: Rift Apart can be made for the PS4, the experience would be completely different from what Insomniac has developed. 

Speaking with the world-wide head of marketing of PlayStation, Eric Lempel, during the PS5 Dualsense controller reveal, Geoff Keighley asked about how the SSD can benefit and impact gamer experiences.

When you look at a game like Ratchet :

It also allows developers new thing, it isn’t just about faster loading times. And you take a great developer like Insomniac, and they found a way to say “okay look here’s a game that could only be made on PlayStation five, on this generation using this technology”. A lot of what you saw on the show jumping through those different worlds instantly just can’t be done in most cases, and it needs new hardware, it needs new power. That’s something we’re looking forward to., He said, “that really speaks to what next-gen is to us”

When asked if the game would be possible on the PS4, this is what Eric had to say:

You would have to change it, you would have to change the way the game works. It would be a different experience, according to everything that Insomniac has told us, this hardware allows them to deliver on this vision, they could not make it. If they did, it woulf just be different. You would be playing a different type of game, and the experience would be different.

There you have it, for those thinking that this is all about simply scaling the game down to make it work it would seem that this is simply not the case.  If you are interested in hearing more news on the game, be sure to visit our official hub page