Why anyone thinks that displaying something like a desktop OS with many static elements is a good idea is beyond me. Yes you can use some tricks to reduce the impact but why should you adapt in this way? I also realise that OLED manufacturers have dealt with burn in to a degree. However, it's not eliminated. The future for PC screens is probably going to be microled, not OLED and not LCD. However, if you're the kind of person who replaces monitors/laptops frequently, maybe burn in is never an issue you will experience.
Preempt is all about interrupting processing in favour of other processes. Unfortunately I was not able to find a good page to explain this after a quick google.
In practice, using RT for a desktop would probably mean performance would be slower, not faster. The overriding purpose of an RTOS is reliable and consistent processing time.
Hackers are just a migratory lifeform with a tropism for computers.