There are many ways to deliver OA: personal web sites, blogs, wikis, databases, ebooks, videos, audios, webcasts, discussion forums, RSS feeds, and P2P networks.
Authors control the volume and growth of OA. They decide whether to submit their work to OA journals (gold OA), whether to deposit their work in OA repositories (green OA), and how to use their copyrights.
Any kind of content can be digitized, and any kind of digital content can be put online without price or permission barriers. In that sense, the potential scope of OA is universal.
Many publishers who oppose OA concede that OA is better for research and researchers than toll access. They merely object that we can’t pay for it. But we can pay for it.
One transition complexity is the fresh convert who supports OA in theory but doesn’t understand how to pay for it, how to support peer review, how to avoid copyright infringement, how to avoid violating academic freedom, etc.