I was long aware of this compression, but was curious why anyone else than Google implement it. Then I found following link: https://engineering.linkedin.com/shared-dictionary-compression-http-linkedin
Wow, LinkedIn implemented it too, looks like it worth the effort for big volume net traffics. So I went with Fiddler to investigate headers which are well defined for this compression, I mean dictionary negotiation, etc. Side note, latest Chrome, latest Fiddler and Chrome reports "Accept-Encoding" sdch as well as the rest - gzip, deflate
Guess what? I dont see it working, nor for Google (search queries) neither for LinkedIn. Nada! no dictionary negotiation, no download of dictionary, no server reporting it has a dictionary for the browser to download. So what happend? Is it dead? abandoned by Google and LinkedIn? It proved to be inefficient?
Short answer - it is dead for now