How about _simulation_ mode in GNU/Linux? .....

So that a user can perform a whole lot of operations and actually nothing is touched - the end result would be as if there were an extra hard disk on which to try out your experiments, without affecting the core system, and then commit all that to the main system if you think it is all ok.

AFAIK, Transactional filesystems can do all this. But, this is also probably needed for the desktop Linux distro. Maybe something like a git-filesystem aka gitfs?

Motivation: 

So often in pathetic operating systems I have found elementary processes like copy and move failing, just because there is no pre-calculation/simulation mode and some system file, halfway through creates a problem as a result of which the entire process is abandoned half way with no indication of what is spoilt where and there is not rule or pattern to the resultant chaos, so that some recovery becomes possible.

Keep it optional or switched-off by default if it is bad for speed.

There is another obvious, compelling reason for this: 
multi-core CPUs or multi-chip Mobos/systems with some parts of the processing power unutilised at any time.