You're more likely to choose a weak one than not. I can create an issue if you want to produce the passphrase or entropy yourself.

k00b

Any reason we can't choose our own passphrase?


SimpleStacker

This should encourage some to use two. 
Just in case the unimaginable happens. 

I'd guess on average multi-device people have a desktop/laptop and a phone. Many people just use one device though I'd guess.

Okay, thats not too bad then. 
Most people have at least two devices on, right? 

Also if you lose the passphrase, but one device is still connected, you can reset device sync on that device without data loss.