Something wich I found cool in RWPaint is that your file explorer is integrated in the main window, it does not open a new window as such.
A mockup idea
https://i.ibb.co/DYWGyvd/imagebrowser-mod.png
I get the idea, though I am not motivated to do such change because it is already nice. I don't mind my software being a bit different.
The "save" dialog wastes unnecessary space
https://i.ibb.co/09BQ5TF/savedialog.png
Another mouckup idea
https://i.ibb.co/KyMnbXY/savedialog-mod.png
Well that works in this case, but save a JPEG and more space is used on the left side.
That said, I agree it would be nice to have network access.
About having Desktop, the thing is I did not find a consistent way of getting the Pictures directory on Linux, so I have put by default the user directory. So it is kind of a generic default directory. From there you can go to Desktop or Pictures.
On Windows, I there is a consistent way of getting the Pictures directory so I have put that by default, and from there you can go one directory up and then choose any user directory. As path are easily accessible on the right part of the screen, I guess it is ok.
I did not want to make the interface too different depending on the system by adding special buttons.
Though if we start adding Network shortcuts, then why not try at that point to make a kind of dynamic list of shortcuts that could include any OS specific ones.