Thank you for this comment!

I'm in the IT industry, and things are probably partially different. A big part of the content is renewed, so must the corresponding course material be.

Obviously, with time there is a growing part which is stabilizing. For example, Microsoft Word is no new subject anymore, even if new versions continue to come in. Idem for the basics of algorithms taught in the universities, the same way for decades now.

But the most successful courses (paid by companies) are on new technologies, and I see no slow down in stuff that men invent and that programmers must learn.

It sets the need for a dimension of contributing authors, where no text book exists yet. Because even when one to ten brand new books exist on a technology, they are not mainstream at all. If they were to be rewritten 2 years later, they would be quite different. And these are no class books, they are not meant to be used in a classroom (on-line or not): no exercise, no summary, no pedagogy — just a scientist explaining his new technology…

My point is that for IT training, there is a new dimension to invent: some kind of wikipedia for course book, written, improved and maintained by the teachers (and students…) of an on-line learning community.