The business of creating and selling textbooks contributes to the mediocrity of textbooks, but the medium itself still has potential.
What options aren't possible using an existing text? Many of the shortcomings of existing textbooks are artifacts of the creation, licensing, and distribution mechanisms of traditional textbook publishers, and not of the textbook itself.
The licensing structure of textbooks interferes with remixing, interaction, and reuse; this is a business problem, not something inherent in the medium.
The medium (print) drives up cost, creates the practice of remaindered copies (and the cost of remaindered books is factored into the price of the book) and creates a need for "updated" editions. Print on demand mitigates this to an extent, but a version of a text where the digital copy is always accessible makes this problem smaller still. Textbook manufacturers could be providing access to digital versions of the latest copies now, but their business model doesn't allow for this type of transparency (One notable exception to this is Flat World Knowledge, who puts current versions of their texts online, under a Creative Commons license).
People talk about reinventing the textbook. Too often, this is code for "discovering a business plan that helps us license, sell, and profit from content." As we talk about creating the next generation of texts that support learning, we need to focus on what worked with existing texts, and what didn't. The pedagogical need must drive what textbooks evolve into. The existing business practices of textbook manufacturers are the chaff that prevents textbooks from being as useful as they could be. Alternative means of creation and distribution - that allow localized solutions to specific learning contexts - provide a cost-effective way into a new phase of what learning can be.
So, when I read announcements where a person describes a planned text where "a student would watch some things, read some things, but most importantly, do some things" I need to wonder: given that open content supports precisely this type of learning, why do we need to "create" a "new" textbook to do this? The next iteration of texts that support teaching and learning need to be shaped by the needs of teachers and learners.