This question pops up in the forums at least once each year - the latest incarnation is here
The consensus of opinion each time is probably never. The above link contains some technical discussion as to why this is probably the case - calculations and animations would be very CPU intensive with resulting poor FPS performance on most systems; lack of technical data in config files on deformation and behaviour under stress/strain of virtual construction materials used in rolling stock and buildings etc - are just two of the issues. Without those sorts of details and other matters, the crashes are always going to be "unsatisfactory" and "cartoonish".
Then there is the point that Trainz is a train simulator, not a crash simulator. It seems that only a minority of users want full crash simulations at the expense of better performance and features in other areas.
I like when a 135 car train is driven off a precipice, into a pit, and the railcars keep jumping up and down like Mexican jumping beans ... trying to escape, like a lobster from a hot pot of boiling water
