They should just copy Google's voice software, its beats Siri to death in terms of voice recognition.
Siri almost never has issues understanding me. She just sometimes says that she's not available for some reason. 4 bars of LTE, Siri, what else do you want?! I usually use it (not going to say "her" here XD) for navigation, which brings me to the problem of Apple Maps having good directions but very few POIs mapped in.
Google's voice assistant can't understand anything unpopular I say to it. It seems to correct any misunderstandings with Google search recommendations, meaning that it works amazingly well if I'm Googling something common but can hardly understand anything uncommon. I envy those people who say that Google answers all their questions because it's usually not the case for me. "How do you use x264?" "How do you compile X for PowerPC?"