No -- downloaded demo doesn't work, local web server doesn't work.
"..may come back to this at some point in the future.." . This baby isn't getting any tender loving care then. Sounds more like it's being abandoned.
That's very odd... the online demo runs for me on every computer I've tried. I'll take a look at this over the weekend and see if I can get it functional for others. From what I've read, a web server is ABSOLUTELY mandatory as if it tries to load image files locally the browser blocks it for security. I'll try and figure out what's broken tho.
EDIT: After asking a few people to test for me I've been told it works completely fine on their ends using Python to host a local web server. Make sure you've downloaded the complete zip of the Github repo and kept the file structure absolutely intact after extracting. I've added instructions to the Github page on how to quickly launch the project using Python as a webhost. It's been tested on Windows 10 with both Chrome and Firefox, unfortunately I don't have access to any older operating systems like 8.1 but I'd expect it to work.
I'll go ahead and try uploading the project to an actual p5 account and put a link to the sketch on the page , that should handle any client side issues and let it be completely editable within a web browser.