After considering full device encryption for Android 5.0 phones and tablets earlier this year, Google has decided to enforce the requirement with Android 6.0.
New phones shipping with Android 6.0 Marshmallow software and meeting a certain performance standard must be encrypted by default. Android Police reported the change in Google's most recently Android Compatibility Definition Document, where it states:
"For device implementations supporting full-disk encryption and with Advanced Encryption Standard (AES) crypto performance above 50MiB/sec, the full-disk encryption MUST be enabled by default at the time the user has completed the out-of-box setup experience."
Older devices that get upgraded to Android 6.0 in the future -- here's a running list of them so far -- have a bit of an out, according to Google, which says, "If a device implementation is already launched on an earlier Android version with full-disk encryption disabled by default, such a device cannot meet the requirement through a system software update and thus MAY be exempted."
Last year when the topic of encryption arose with the Nexus 6 -- it was encrypted by default -- there was talk of reduced device performance.
That could still be the case but it's too soon to tell until proper device testing with read / write flash storage speeds. Regardless, many would argue that personal data security is worth more than a slightly faster device.
That actually raises a question: Android typically provides more options for user choice than other mobile platforms. Will removing the choice of encrypted vs unencrypted data from the user be an issue going forward?