Currently, if you are reading math and hit something you don't understand, you can refer to other references (which may not use the same notation or approach things in quite the same way), and/or try to work out the details yourself, or get help from someone else. Working through yourself and looking at other sources certainly helps one learn, but can be very inefficient, and there can be a high energy barrier to success.
A 'zoomable' math text would require a lot of work to create, but the writing could be done collaboratively (or even partly automatically). There is some software to be written to implement this idea, but given the large number of computer and other scientists who depend on learning and using math, it is surprising to me that there hasn't been more experimentation with different ways to present it.
I guess I should try to write it...