Finally, I think Actions are great for animations, because you will definitely need to apply the same logic to many different elements. One of my favorite examples are FLIP animations, where a change in DOM position can be animated. For example shuffling a list of items. I will not dive deep into the topic in this article: I've written about some techniques in this article about FLIP animations in React and in this article about how to create spring animations with Web Animation API. Although they are not about Svelte, at the end of the day it all boils down to manipulating the HTML element directly. And Svelte Actions are a great place to do it.

For user-contributed data that's freeform and unstructured, use jsonb. It should perform as well as hstore, but it's more flexible and easier to work with.