Why would you want to do this? Well, if you’re working on a project that’s not 100% ExtJS from top to bottom, it’s likely you’re using ExtJS along side other frameworks and cherry picking the best features as you need them. For example, at my current job, we use ExtJS for grids, forms, some data bound components we’ve built out ourselves and of course the accompanying stores that stick it all together but we don’t use ExtJS to provide a “single page app” in what may be considered the usual ExtJS MVC approach when using 4.x+.
So I decided to just give it a go and see what happened. After all, worse case scenario is I lose a little time working on a mini experiment that goes nowhere but teaches me at least something.