I think they should go after 3) if this gains traction. They already do 1) BUT it requires considerable amount of effort from their side and the authors are not

I think they should go after 3) if this gains traction. They already do 1) BUT it requires considerable amount of effort from their side and the authors are not always interested. However, getting a cut from each rental would be quite lucrative and won't require them to keep churning new editions out.