For example, a project where you could mess around with your own photos with Graphic Effects. Some kind of upload button inside of Scratch? Or just any way to get outside images into a Scratch Project.

As a suggestion, Maybe even a new block like so:

As of my knowledge, there is no way to use a Scratch project as a means to upload images. I don't see Scratch Team implementing this feature as;
1. Someone can use cloud variables to upload inappropriate pictures (which is sort of why chatroom projects are banned),
2. It would be very complicated to code into Scratch and ST is more focused on accessibility updates rather than entirely new features anyway.

The only way to do it yet is to press “See inside” and add a costume to a sprite. Some projects use that.

Really the only input you get (excluding methods that require going into the project) is the ask block, which takes text.
With this method, you'd have to convert the image into text outside of scratch. I personally either use my own python scripts or hex editors to convert data into something readable. Another probably better option is: https://xeltalliv.github.io/ScratchTools/Img2list/

You'd still have to implement ways to store and display the data in scratch, which usually can be done with lists and the pen extension. You can see my image editor project as an example.
https://scratch.mit.edu/projects/552647396/

Cool