Of course Apple did not "hijack" anything: full screen support has always been strictly opt-in. But apps would feel pressure to adopt the system implementation.
This doesn't make much sense, does it? Obviously apps adopt the system implementation. The problem the OP is talking about is that the system implementation became pretty weird, broke some apps that used to work just fine (especially lots of xquartz ones), and thought that the best use for your extra monitors was to just display a dark gray pattern.
Personally, I learned to live with it (sigh, uncheck "displays have separate spaces"), but it does seem like a good example of Apple shoving a half-baked idea out the door.
This doesn't make much sense, does it? Obviously apps adopt the system implementation. The problem the OP is talking about is that the system implementation became pretty weird, broke some apps that used to work just fine (especially lots of xquartz ones), and thought that the best use for your extra monitors was to just display a dark gray pattern.
Personally, I learned to live with it (sigh, uncheck "displays have separate spaces"), but it does seem like a good example of Apple shoving a half-baked idea out the door.