My idea is:
The old builder used what I understood is elfinder. The new builder does not use this. The new builder also does not show any content in the assets section.
I would really like to see some kind of image management functions including foldering. Creating even a dozen or so emails with images is going to clog up the image popup window making locating the right images difficult. I have devised naming conventions to help avoid this problem but if one person does not know or understand the conventions, headaches all around.
With regards to foldering. There is always reusable content that would need to be found for multiple emails. Having those reusable images in a folder to quickly locate and insert makes things easier.
I think these groups of people would benefit from this idea: Everyone
Why I think they would benefit from this idea: Ease of use