The three distinctive features of the Amiga:
- revolutionary custom graphics hardware
- better sound hardware than competitors
- pre-emptive multitasking
Therefore, if I was attempting something like this today, I would:
- make the graphics preeminent in the system. In other words, keep the graphics card and throw away the legacy CPU. Let it drive PCI devices.
- on its own, doing that makes it much harder to program, so put considerable work into making the instruction set and programmer's model open and well documented
- find a DAW engineer and let them build the audio subsystem with an obsessive focus on low latency. Let's aim for no more than 10 samples latency between input and output processing and see where that gets us.
- full multitasking in which nothing is ever allowed to block anything else unrelated, through resource reservation (qv the Nemesis research operating system). Having an Electron app on the system should not impair anything else, and the system's default editor should also be focused on low-latency.
- apps are by default fully security partitioned from each other. The operating system would maintain a CRDT-based record-orientated personal data storage system, incorporating lessons from PalmOS. This gives both native sync and automatic persistence across power-off.
- low latency non-USB keyboard and mouse. PS/2 would actually work but we could go for something really surprising like gigabit Ethernet or optical TOSLINK.
(Low latency is a good example of a feature which is extremely hard to retrofit and you end up redesigning the system around it).