Can anyone make a community wall and post it as a thought for use?
absolutely! the more the better.
The artist creating the background wall chosen will be the one to upload the final wall(s) to the library. The reason we went with 1920 x1200 as the base size is so it can be downsized to the other various resolutions.
Background artists should keep this in mind and possibly leave a bit of "non signature" area on each end so that going from 16:9 to 4:3 doesn't require cutting off anything important. IE windows or gates or a corner.....you get the idea.