Actually, if it has true support for async and better graphics, the UI can be modified so it is "perceived" to have better speed. In the current Emacs, some actions are slowe and we know it has nothing to do with Emacs as they depends on external processes. But it makes entire Emacs hang, and it's terrible from user perspective. If there is a way to make those operations running async, with some nice text messages/graphics to indicate the status, it would be much better. It is similar to the story about installing mirrors inside elevators and made people feel waiting time is much shorter, while travelling time was actually the same.