Yes, you can lay the PS5 on its side
Sony finally revealed what the PS5 will look like and what games are coming to it. The wavy black and white box does look different than the other PlayStation systems especially in how Sony decided to show it off. The reveal video almost exclusively showed it standing up. However, given some alternate pictures, Sony has revealed that you will also be able to use the PS5 horizontally.
These alternate pics came through in Sony’s press release photos. While most show the console standing up, there is indeed one glimpse of it laying horizontally as you can see in the above picture. That picture shows the disc-version of the PS5 as you can barely see the disc slot underneath the top flap. The picture below this paragraph shows the disc-free PS5 on its side.
The curves do make the PS5 sit unevenly on a surface when laid on its side. In order to balance that out, it looks as though you can take the stand and slide in underneath to even it out. The less curvy, disc-free version of the PS5 has a slimmer stand, after all.
Being able to play the horizontally puts it in line with the other PlayStation consoles as most can be played either way. It just looks like it takes a little peripheral to get to the same place.