A few things I'd love to see
Just going to leave these here in case you're looking for ideas :-)
Apologies if they have been mentioned in other posts.
I would love the ability to add some kind of "meta" model to every single field, that could maybe be accessed in the UI by clicking on "advanced" and showing a popup or something. I would use this for example to add a checkbox to every text field for "index in search", or a numeric field for "search index priority".
Very similar to above I would love to be able to add extra fields to media assets. The description is probably always used as alt text on an image, but in the current project I'm working on I need to add image attribution text. It would be nice if I didn't have to add that as an extra text field in every model where I add an asset. Also it mean the attribution is tied to the asset itself, so I wouldn't have to find every content item where that image is used to make updates to the associated text.
I would love to also be able to restrict the types of items that can be added in the rich-text modular content.