Earlier quoted context omitted.
The proxy icon is still there, it seems you have to hover or click to show it though.
So discoverability is finally replaced by the "Ahhh" paradigm?
I love the proxy icon, too, by the way. But it's always been a badly documented, surprising, quirky feature. I found it by accident, by slipping and dragging a folder onto the menubar. That's not even useful; I didn't understand what I'd done. Eventually, after reading blogs and manuals, I use the proxy icon (and the brilliant Findersave dialog tricks) all the time.
I don't think we gain much by framing the argument around "discoverability" any more. I think it's much more useful to talk in terms of the overall interface paradigm. The proxy icon kind fitted into the "desktop" paradigm - i.e. a scatter of media and tools strewn across a desk. But Apple are moving away from that, and into a new paradigm of "surfaces for interaction". The i-devices have been in that space for years. The "mac" devices are now going there. Both are gonna change again, bit by bit, in the future as humans develop new ways to interact with this weird networked functional data thing they've created, and Apple try to provide novel tooling for novel technology. They do seem to be going faster, and breaking more things, than they did in the 80s and early 90s when they lead the desktop paradigm. They're possibly experimenting with ideas on the wider user base, rather than doing closed door research. A big part of that is due to the wider user base being MUCH more comfortable with computing than before. People with very little "computing" training are contributing daily to the development of digital culture.