The only downside is some backtrace might be lost. But I don't think that is a big deal. Crashes during shutdown are rare cases nowadays(Ihope I'm right), and users noticing those crashes only hours later arethe rare case in rare cases (but very annoying).
I regularly get them, most times something Kontact related. What about just saving the backtrace to disk? Next step could be on next startup to check if there are automatically saved backtraces and ask if to drop/save/report them.
