I agree a decent guide would be good. In the meantime I think just playing around with Ember CLI on a separate or experimental project is a good place to start. There will probably be innumerable little questions that come up as you try to get familiar with Ember CLI.
It would probably be helpful to create a reference app and show both before and after. Preferably in the same git repo. Perhaps the TODOs app would be a candidate. But I would love to see something moderately more complex.
Personally, I went from ember rails → Ember app kit rails → Ember CLI
A couple high level observations:
Get used to modules and node.js and NPM ecosystem. A lot different than the Globals (App.SomeController, App.Route, etc). Ember CLI puts a big emphasis on file organization and requires that you explicitly import related modules (including Ember and Ember Data).
Ember CLI supports live reloading, and you can proxy to your rails server as well. Ember CLI works really well when you think of your rails project as simply serving up API. You can launch your rails server on port 3000 and then have Ember CLI serve up the ember frontend code on port 4200 and then proxy over to the rails backend. This is all done through node and Express. Frontend and backend can in fact be separate projects or worked on in isolation.
ps it is Yehuda, not Yakuda.
Also, I believe the core team is working on a migration utility for this very problem. Something that will auto migrate from old App globals style to Ember CLI modules style.
Some places to start
This might be helpful too