Ilmari Karonen wrote:
The hardest part would be restructuring the thumbnail repository to allow thumbs in multiple formats to coexist.
The thumbnail repository is made of folders, and thumbs keep their format extension, so Having 800px-Example.jpg and 800px-Example.png wouldn't be a problem. However, i think there was also a SQL table indexing them, which may need some little changes. Also the auto-thumbnailing script (should be easy).