Like another comment pointed out they seem to store pins as a JSON blob in a single column anyway. They probably should've used Drupal.

Really, this is pinterest. They store 'boards' and 'pins', you may as well have a bit of fun with it. What use cases do they have for the features you list? They probably only used a database for write transactions?

I deeply value database technology and use it daily, but I don't think something simple like this needs to worry too hard about it.