Given how often diagrams / photos etc are used in the best answers, is it possible that the upload could be made one step, so image and pasted link address are uploaded in the same dialogue box?
... that can't be done with our current third-party file picker.
Assuming that I understood your question correctly, the image source can't be added in the same dialog box as the URL of the image because that feature is not built into the file picker.
The file picker itself was not built by the team--it's a third-party application, much like the graphing utility--so they couldn't really make any changes to it [as far as I know, it's not an open source application].
So in order for the team to make this change, they would have to ditch this file picker completely and either build one themselves--too resource and time-extensive--or look to invest in another file picker--not really an attractive option at the moment, either.
Long story short, we're pretty much stuck with the current file picker, i.e. we're stuck with having to upload the image and add the image source in two separate steps.