I use 1Password instead of iCloud Keychain because, even after I unlock my iPhone or iPad, anyone who wants access to my passwords or credit cards still has to unlock 1Password. Like iTunes and Apple Pay purchases, it uses Touch ID to secure it against anyone but me. So, if a crying stranger asks to borrow my iPhone to call home, if a friend asks to surf the web while they wait, if someone at a conference has a failure and asks to borrow a device, I can hand it over without worrying about passwords or credit cards. You might think I'd like Touch ID for iCloud Keychain, and you're be right. But what I'd really like is more. I'd like a Guest Mode.
Adding Touch ID to iCloud Keychain would make iCloud Keychain more secure, but like 1Password it would still only protect login, credit card, and a small subset of other data.
What if the person I hand my iPhone or iPad to decides to go snooping through my photos or messages? Apple could add optional Touch ID to every app, so you could go into Settings, flip a Secure toggle, and then have to pin or fingerprint your way into any built-in or App Store app. People and institutions highly vested in security would no doubt love that, but it would add both complexity and an excessive amount of overhead.
A Guest Mode could be a simpler, more elegant solution.
With iOS 8, Apple refactored its system manager, SpringBoard, into several smaller, more focused components. In addition to BackBoard, which was already spun off to handle background tasks, they added Frontboard for foreground tasks. They also added PreBoard to handle the Lock screen under secure, encrypted conditions. Whether by extending Preboard or by creating a GuestBoard, if such a thing made any sense, perhaps iOS could provide a more functional and yet still secure Lock screen.
Right now, if you don't use Touch ID or enter a passcode, the Lock screen presents you with an Emergency option. It lets you call 911 or whatever the emergency number is in your area. With iOS 8, if enabled, it also lets a first responder pull up an Emergency card from the Health app with vital medical information like drug allergies.
In addition, a Guest button could allow access to a secure instance of the Phone app, so that crying stranger could call their parents, or Safari, so that bored child could surf the web.
"Secure" being the key consideration. Lock screen is perpetually torn between security and convenience. You can enable features like Notification Center, message previews, Control Center, Siri, Passbook, and more, and each one provides convenience at the expense of security and privacy. They also expose Apple to potential Lock screen bypasses.
Just like you can disable features from the Lock screen, disabling the Guest Mode would allow for individuals to better choose their own balance. Perhaps you could require Touch ID or a passcode to enter Guest Mode, so that someone who takes unauthorized possession of your device couldn't abuse it.
You can currently implement something like this using Guided Access. You can lock your iPhone or iPad to Safari or to a game, and have it stay that way until your passcode unlocks it.
It takes time to set up, however, and it's not ideal in all situations. With Guest Mode, if enabled, you could just swipe, tap, and hand over your iPhone or iPad without having to worry about anyone accessing anything else that's on it.
You can be a good samaritan with less risk of bad things happening.