We can do all necessary ui elements already via events, they're just super annoying to put together.
I don't think we should be trying to get Scirra to implement their own versions of gui parts however. The existing forms serve as an example of why. They get the basic job done, but are terrible to customise.
Its likely the same will happen to any other elements made by someone else. Those types of things will never be a perfect fit for everything.
I think ideally we need to have some sort of push to get a bunch of different plugs made by a bunch of different third party developers to fill that need.