trace mode. Have it save the data of aliases and functions the script has called and save it to the disk. It would make it far easier to catch crash bugs. I have some people who keep hitting a crash bug almost randomly. But all using the same script, but with script it's almost impossible to figure out what exactly is causing. If it saved the entire "called this function" "called this alias function". It might be nice to have the last few things it does before it dies.
Although, it would slow it down a lot with all the writing to disk. It would not be on all the time. But, if it happens the log would pretty much isolate it in no time. And with saving the input make it quick and easy to find repeatable code to crash mIRC and avoid such code.