running every player in a thread for himself would cause lots of problems and synchronization overhead...
it is not something one can easily implement...
Also there was a discussion some time ago if mangos should go the mutlithreading way (1 executable) or the multiprocessing way (several executables for each part of the world..), but I don't know how it ended.
anyway I don't think its appropriate to discuss this here... also your request looks like one can pull this off in 1 week. It is really something that is way harder to implement than you think and may take some time...
Bottom line is, you will not see something like that in mangos for at least some months
(also what is there is not a crash but a failed assertion.. a programmer puts it somewhere where he assumes that some variable/pointer has to meet a certain condition. When this is not the case you get that error... its not really a crash...)