You can already do it...
You can download a single frame or download the whole project (menu in the top right corner).
Obviously, animations are supported by the rendering system but not the workshop so both button will download the one frame of the project. You can see the difference in how the zip archive is structured though.

It would make rendering on ipads a lot easier if you could download a png, not a zip.

It is still possible to do it though. Developing and maintaining redondant code cannot really be justified here.

Can you explain how? Thanks

I just use one of the free unzip apps. I think it is called izip.

OK, thanks, I'll check it out.

Hmm, when I click on the project tab, and then hit download, it still only downloads one image--the one currently displayed. So could you clarify what this does exactly? I'm still confused as to how I can download multiple images.

This is what I explained above. The end result is currently roughly similar as projects currently only contain one image. When animation will be a thing and a project will contain multiple frames you will see the difference.

Okay, if I understand correctly it's only for animations then.

Yes. You can not download all your projects with one button. It doesn't make any sense and I definitely don't have the server power yet to zip multiple GBs of data (mainly due to OpenEXR files).

Please excuse my confusion and lack of knowledge on the subject. All I was saying is it would be nice to be able to select more than one rendered image, and then download them all as a zip. Rather than downloading a new zip for each rendered image. I am still not clear on what a 'project' is. I don't think what I'm talking about would take gigabytes of data... #Still Confused