The command pattern is/was a recommended pattern and is a massive step forward from building an RPC interface using the RemoteService and RemoteServiceServlet which is pretty much all that was available at the time of the Google I/O presentation you refer to.
The GWT-RPC approach is very good and works well and provides the batching and undo mechanism. I have to say I've never implemented a single undo() function on any of my handlers although I do make use of batching.
A newer approach would be to use RequestFactory and map your code onto your service. This does support batching but not undo. It's not a great deal of work to implement but does have its peculiarities. A nice example can be found here.
If you need a REST interface then making use of this in your GWT to save developing two interfaces seems like a sensible idea. But as @Riley Lark says you'll have to write your own batching (and undo() if you need to).
My feeling is that both batching and undo don't really fit with the REST approach, but that's just my opinion. There's some more info here from a similar question.
Perosnally I would probably make use of GWTs infrastructure and RequestFactory to do client to server comms and take advantage of the batching and the optomised protocol and the cross site scripting protection and write a separate REST interface for whatever needs to use it.
