O'Reilly has (or at least had) such a library and I seem to recall them picking up titles from other publishers. The problem is that it was rather expensive, though they did offset the cost by offering a few credits every month to buy books. It also worked well in O'Reilly's case because they catered to a particular audience and offered an extensive library to them. I'm not sure how well that would work for an audience who reads for entertainment, and may be reading books from multiple publishers.