Use case or problem
I often want to have callouts as default folded for keeping a lot of content inside a note tidy. I use headers also, but prefer callouts because their folding state is more reliable and they are less hierarchical than headers and give more ways to visually distinguish things from another. Having callouts closed by default means that when I link to them and then hover the preview, it only shows the folded callout, but not the content inside of it. Folded headers will still display their content even if their last state was folded.
Proposed solution
Make the preview behavior for callouts the same as for headers by having it show the content even if it is defaulted to a folded state