I kind of like having one window per application. I already have 15 different applications open at the same time, I don’t need them to have 4 windows each.
I am a bit ambivalent on this. Most of the small windows in the mock-ups would actually be palettes, not true windows. It also works much better in an application-centric OS such as MacOS compared to window-centric ones like Windows or most Linux DEs.
Sure, the proliferation of floating palettes in the 2000s was a bit much, but on the other hand monolithic single-window apps for everything is terrible. Slack, for example, would be much better if we could different windows for calls, chats, and the channel list. As it stands now, we have either one window with conflicting functions, or a lot of repeated information taking up quite a lot of space. Ultimately, this is the result of cramming everything into one window because some OSes confuse windows for applications. It is grating to see this design pattern on macOS, which really does not work that way.