Something that is not to underestimate is the amount of work it takes to support various kinds of content and programming languages nicely in this form. To get

Something that is not to underestimate is the amount of work it takes to support various kinds of content and programming languages nicely in this form. To get the most from it you want some kind of runtime integration to get feedback (errors completion) or at least good type system support integrated. It's interesting to watch a project like Atom grow – the plugin system they have is nice but ultimately the kinds of interaction they support with it are only text based. I think, in order to have a Smalltalk-like IDE take off, one needs to have similar support for extensions while allowing those to be easily integrated with richer tools like inspectors and debuggers.