There is the Ext.app.EventBus that is a private class included in the Ext.app.Application instance. I think that is where it stores the component query selectors from the Application.control configuration parameter when you create an application. I don't know if it's enough to fully implement the mediator pattern since the control queries only accept components and will not allow you to attach events to classes that you have implemented the Observable class/mixin in, but it might server your needs. I imagine something like the MsgBus will still be necessary if that is the pattern you follow when writing complex apps.
There is the Ext.app.EventBus that is a private class included in the Ext.app.Application instance. I think that is where it stores the component query selectors from the Application.control configuration parameter when you create an application. I don't know if it's enough to fully implement the mediator pattern since the control queries only accept components and will not allow you to attach events to classes that you have implemented the Observable class/mixin in, but it might server your needs. I imagine something like the MsgBus will still be necessary if that is the pattern you follow when writing complex apps.