You can do very simple comparisson actually to this gen.
March 2012 - HD 7870 (which is, more or less, what's in PS4) - 175W - $350
July 2019 - RX 5700 - 180W - $379
That would put PS5 at $399.
If there is some additional hadrware block for RT, that would be somewhat decent, though still pretty weak for proper transition to 4K.
But an RX5700 wouldn't put the PS5 in the range of a 2070, which was my point. Add to that the additional possible chips and their super duper SSD it's easy to see that we won't get 2070 levels of performance on a $400 price point.
I wish Sony would just put out an expensive version that has the hardware cranked up and costs $500 or more but I'm not holding my breath. The thing is, even with a 2070 doing 4k60fps is a very tough ask. I believe lots of people are expecting to see 4k60 across the board and they're gonna be very disappointed.
Honestly, no idea how RX 5700 will perform - on paper, when you look at all the specs, it should be able to perform as well as 2070 - but I have no idea if their architectural improvements finally managed to put them at nVidia's level of efficiency
As for 4K60fps - it's possible, but pointless if they want any significant visual improvements. For PS5 and Scarlett to have same leap as PS4 to PS360 (roughly speaking), when it's all taken into account (generational visual improvements and resolution bump), we should be talking about 22+ (GCN1) TFLOPS, and they won't be anywhere near that.
Personally, due to those SSDs, I mostly hope for at least some lateral moves in next gen - specifically, navigating massive voxel octrees would be possible, and that would make for fully destructable, yet persistent worlds with fairly fine resolution.