In this vein, I think they tried to do too much at once. They should have learned their lesson with the PowerPC. They had two tracks, one was trying to implement a new OS. The other implemented the 68k OS on a simulator. The first track was way late. If Copland could have released just a protected environment at first, and allowed people to start writing for it, they could have added all the rest later.

If you look at the Copland technical docs, they describe an OS with modern underpinnings but running the Mac UI as a single process on top of it (https://en.wikipedia.org/wiki/Copland_(operating_system)#Cop...). Developers were supposed to put as much functionality as they could into background processes/threads that would benefit from preemptive multitasking and protected memory.

Amusingly, classic Mac OS ended up sort of close to that if you squint. It had a "nanokernel" that ran tasks preemptively and even supported multiple CPUs, but like with Copland the entire UI ran as a single "blue" task. The main difference from Copland as far as I can tell is that non-UI tasks were heavily restricted in the OS APIs that they could call; for unsupported APIs they had to send a message to the blue task and wait for a response. More details at http://mirror.informatimago.com/next/developer.apple.com/tec....