in my experience (and this is by using my eyes as debuggers) there is no real reason behind client crashes. (not for the previous reson) There is also no good reason to make a program that you have to recompile, and I have seen many perfectly fast examples (good luck finding them).
Back to the name of the post, physics info can be transferred by seperate reader/writers* that are extremely small and are virtually invisible - therefor no hacks are possible. And they can use the lowest level, binary, to communicate, so no huge data transfers.
Also, packet tracking, by putting ids on each item sent online will keep creatures from pseudo-rubberbanding. You just make sure that the \'client\' only accepts the most recent i.d.
As for recieving attacks, since it is easy to detect whether you are in battle or not, a reader/writer can be loaded for each individual battle, and send binary (meaning very easy communication) signals for ragdoll stuff.
To those innocent bystanders, if the system detects that you are watching the battle, then it loads the reader/writer and feeds you the info. If not, you only see a simple distress animation in the corner of the screen.
By the time this game needs any of this, there should be a movement for adding servers. Each server could take care of each individual system, like earth, gravity, combat, sky, chat, wind, water, plants, etc. This way the server vs. players ratio could be cut down.
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*reader/writer is not the standard name, I have never heard of them, I know they exist the way they do because I could program one.