On page 16 of the New Features Guide in the section about sharing OM between projects, it says:
Deleting optimized media from DaVinci Resolve now must take place manually, by removing the files in the CacheClip/Optimized Media folder in your OS. There is also currently no way to show which files in your project have been optimized and which have not.
...which is a bummer, but the new Proxy media does list a filepath.
So it seems to me like the new Proxy media is the old optimized media with a new name, and unchained from the .dvcc proprietary management. But then, I'm confused about what the new OM is. It's shared between projects, which is cool, but at the same time, Resolve doesn't know where, or even IF it exists?!?
*EDIT*
Ew. The new Optimized media is the old .dvcc, stuffed into a non-human-readable directory, and unlike before, *without* an info.txt file to identify it. There's no way to manage it from within Resolve, and no way to identify it from the Finder/Explorer, so if you're going to delete your optimized media, you're going to either take your chances with getting the right project, or delete ALL of it. It seems like they're pushing towards user-managed Proxies, which is what people coming from other NLE's are more familiar with anyway.
C'est la vie.