I cobbled together a similar service [1] a while back, but lost interest since I figured it wouldn't be profitable. FWIW the tech behind doing something like this is pretty simple, in my case a small shell script that uses imagemagick to dump the frames of the GIF as well as its framerate and then pipes into ffmpeg compiled with x264 and libvpx support.
[1] http://www.qwikgif.com/