Suggestions:

Perhaps add a command that will upload a file to specific space on a FTP server, with an option to do so after each edit? I'd like to display the pixel art on my website and this seems the easiest way. I can go in and export it and then download, rename and upload, but it seems a schlep.
Could park the FTP credentials in the config, just dunno if t's possible for the server to actually do this. 

Suggestion : Have a admin command that generates a sign linked to the latest auto export. Each time the canvas is edited, it updates those signs links. Dunno how SignArtist stores the image data, but I have seen plugins that link images, and seen them go wrong and paint the same image instanlty on all signs. So updating images on signs is possible, if possibly a tad tricky.