The days of the GWT DevMode are counted. Why? Because DevMode relies on a native browser-plugin to work (that approach was introduced with 2.0 and was called OOPHM, out of process hosted mode). Those browser plugins rely on the C++ NPAPI, which will be deprecated on chrome by the end of 2014. Safari has already disabled NPAPI support (and thus broken DevMode on the Mac + Safari setup). To make things worst, mobile devices never offered such an native API.
Having its days counted, a future solution must be found. The new solution is not new and have been around for while: the SuperDevmode. And interestingly, this solution will work with mobile devices too. So while not new (and there are a few good blog posts documenting how to set it up), there are a few things that me must know.
Secondly, IntelliJ is already working on a remote debugger solution that will probably be released soon. So if you are looking for a tighter IDE integration for future GWT development, it seems like IntelliJ is the IDE of choice.