I think this is an interesting concept. I work in higher education where the cost of textbooks is prohibitive on an individual level. I have personally avoided purchasing textbooks for the MET program because they were extremely expensive and likely to be of limited utility to me. Luckily I’m at UBC Librarian, and I can purchase us print or e-copies of the book and simply check them out – our students frequently do not have this option. All that to say, I’m on board with the central idea of your venture!
The area that I feel requires further fleshing out is the development and curation of content from other teachers. While I am sure that many teachers are excellent writers and developers of content, OER content is vulnerable to plagiarism, non-attribution, and use of questionable sources. When one isn’t accessing what we in ‘the biz’ (libraries;) call high quality evidence (e.g. peer reviewed content whether in texts or journals) there is always the risk of personal bias, lack of personal familiarity on the particular subject, and more. I’d think that in order for a service like this to provide text content of the same quality level as a traditional text, one would have to ensure a rigorous rating service/peer review for all proposed content to ensure the reputation of the service.