Something that would help speed up development of new interfaces would be applications having more extensibility in general. It happens so often that I come across a piece of software where I want to change just one thing, but there's no easy way to do it with plugins or extensions. The alternative is to create the software mostly from scratch myself, which is way too much effort that's just not worth it. Imagine what would happen if you could see all those small changes stack up, we could have so much more interesting functionality.