Hi,
It's not the first time I got a request to add a "IsBusy" handling to MVVM Light. I have not done it so far because I was thinking it is already too specific. Personally I handle IsBusy differently: In every framework I work in, I have a "PleaseWaitControl" and a ViewModelBaseEx with specific features. For instance in WP8 and Win8, which are navigation frameworks with pages, ViewModelBaseEx has additional features around navigation. The "Busy" feature is into ViewModelBaseEx. I also have a PageBase class which does a lot of thing automatically, such as setting the busy state, saving its own navigation state, etc.
In summary, my approach has been to extend MVVM Light with framework specific features in a "Utils" assembly. I have one for Silverlight, one for WPF, one for Windows Phone, one for Windows 8, etc. Sometimes I feel that a feature from my Utils is unified enough to be placed into MVVM Light "core". Maybe the Busy state handling is at this point, I will need to think about it.
Cheers and thanks for the feedback.
Laurent