How many "better JPEGs" have been created now, without significantly displacing JPEG's market share?
There are two really hopeful things about this new project: (1) by leveraging HEVC, we get cheap (energy efficient) and fast decode on future mobile devices and (2) Since he is demonstrating pretty quick decode in JavaScript now, it clearly isn't a CPU pig like JPEG-2000.
I don't necessarily think JPEG is bad, or that it's even Tumblr's fault that I first thought to share photos there, but if any service/software started using BPG I think I would excitedly try it out.
[e.g. http://www.huddug.com/ vs https://www.flickr.com/photos/127341162@N03/15762469070/]