This post inspired me to make Imgur-to-gfycat[1][2], which uses the gfycat api to change <img> tags to embedded gfycat objects using gfycat's embed js, and changes anchors to /fetch urls. It's smart enough to change other anchors on a page if it's managed to resolve a gfycat url, and has a few hacks to work well with Reddit Enhancement Suite.

[1] https://chrome.google.com/webstore/detail/imgur-to-gfycat/id... [2] https://github.com/STRML/Imgur-to-Gfycat