Nobody would adopt them. It's annoying enough to deal with 4 digits when it's cold and I'm wearing gloves and I just want to change the song I'm listening to.

Passphrases suck enough whenever you have to log back in. Are people really gonna put up with that every time they want to use their phone?

On the other hand, if there were a convenient way to toggle between passphrases and 4-digit unlock, (especially if you had to use the passphrases to toggle back to 4-digit) then I would be all for it.

Not really. Have the option to set both a long passphrase and a PIN code.

The long passphrase is used to mount the encrypted file system upon startup, and the PIN code is used merely as a "screen lock", as a casual deterrent from your friends and casual thieves from swiping through your photos before you can catch them.

The file system can be automatically unmounted after a set period of inactivity, or if the user wants to unmount it on demand. After the file system is unmounted, the data is secure again and the long passphrase will once again be needed before anything can be done with the phone.

I'd love to have a long passphrase that has to be entered after booting and every 48 hours, and then a 4-digit pin that's usable when TouchID is for when I'm unlocking my phone with my nose.

Exactly. Short passwords/longish pins suffice for short durations if they are random (i.e. not guessable), particularly if the device requires external hardware to brute force due to attempt duration scaling.

I currently use a generated long password on my Android phone and have adapted to the extra work, but having the option to enter a password once a day and a pin or shorter password throughout that day would be a welcome convenience option, and it's not really significantly more onerous than just a pin.

clearly you're not the average user.

Can't songs just be changed from the lockscreen (i.e., no unlocking needed)? Either way, your point still stands...

A secure passphrase requirement would kill Apple overnight.

Low-friction UI has been Apple's differentiator for years. If you have to take the time to type out a secure passphrase every time you want to interact with your phone, people will stop interacting with their phones (or use phones that suck less).

Why do you think they built Touch ID? Because typing even a 4-digit PIN is too annoying!

They already do, on phone bootup. You can use the fingerprint the rest of the time instead.

maybe if i only needed to use it on boot or daily. inputing a long passphrase is pretty onerous to do all the time.