The framerate thing on PS4 didn't stop bothering so I tried to find out what causes it and I think I kind of did. I don't know the reason, but I know how to reproduce and even avoid it.
As far as I can tell the framerate only stutters if you have a placeable item (like an earth block) equipped and the framerate is (mostly) smooth when you don't. It's easy to reproduce and it's not hard to notice when you look for it. Build a tower as high as you can (above the starting area works well, build a tower by placing block under you after jumping by looking down (L1 or R1)). Unequip the block with the dpad and turn the camera around for a while. Smooth. Now equip the earth block again and do the same and notice how the mountains in the background judder every few seconds. If you're more sensitive you'll see the same issue when just running around and turning the camera anywhere. Nothing equipped: smooth, block equipped: microstutter. I find the difference super obvious. And just to confirm: This doesn't happen at all in the Japanese demo.
Please try it out yourself (if you care) and tell me what you think.
Now the question is, how do we make SE aware of the issue so they can fix it?