While looking into this we figured it an "awesome" bug which looks like was busting the selection of the payload :(  (btw on my macosx the payload was being correctly selected, since the encoders candidates is an unordered array, I guess depending of the environment you can experience the bug or not).

The bug an its resolution here:
https://github.com/rapid7/metasploit-framework/pull/2849/files

According to @mandreko after applying this patch the http/wget method started to work :) He will be testing the cmd echo stager again when possible, there are chances which the same issue was busting the staged payload.