The threaded design wouldn't necessarily be single-process, it would just not have 1 process for every connection. Things like crash detection could still be handled in a separate process. The reason to use threading in most cases is to reduce communication and switching overhead, but for low-traffic backends like a crash handler the overhead of it being a process is quite limited - when it gets triggered context switching overhead is the least of your problems.
Seconded. For instance, Firefox' crash reporter has always been a separate process, even at the time Firefox was mostly single-process, single-threaded. Last time I checked, this was still the case.
