This is correct.

"so-and-so is my wife" => it will update that contact's info (and yours). Then later you can say "text my wife I'm on my way home" and it will.

"call me Mister Smith" => it will update your contact's nickname and use that to address you

"Take me home" (or to work/etc.) => it will bring up directions in apple maps to the "home" address on your contact

If you ask Siri "call my wife" before that, Siri will tell you he doesn't know who your wife is and ask for a contact name, then ask for confirmation, and finally persist the information and proceed with the call.

Right there you highlighted the biggest issue most people have. They're scared to touch or change anything in case they mess something up.

All devices need a universal undo so you can change something and easily undo if you get it wrong or you just preferred the old setting.

For security you could prompt after a while to make the new settings permanent and delete the snapshot.

And if you think people are terrified of messing up the iPhone itself, they cower in mortal fear at trying to do anything in iTunes, which is still, a decade on, inexplicably the only way to do many things with an iPhone (like, for instance, back it up if you don't trust your personal info to iCloud...)

Talk about a feature my 89 year old grandma will be terrified of.

Jane will find it funny if you say “call my wife” and it calls someone else instead I’m sure.