It sounds like:
* you may have to install the ReadCube reader to view the protected PDFs, unclear if you can view them in a regular PDF viewer. ("ReadCube (...) will be used to host and display read-only versions of the articles' PDFs")
* only subscribers can initiate access sharing of specific articles, going back only to 1997 for individual subscribers. It sounds like the general public will not be able to search for articles and view them through the Nature website.
Well, it's a step forward.