We have known for quite some time that the next incarnation of Android will pack a kill switch. This feature has long been requested, as it would prevent unauthorised reuse and, therefore, make a serious dent in smartphone and tablet theft. It is even imposed under Californian law, going into effect next year. But even though Google has not mentioned it yet, the kill switch is indeed baked into Android 5.0 Lollipop.
The kill switch in Android 5.0 Lollipop is officially known as "Factory reset protection", and is offered as an opt-in feature which only works in conjunction with a passcode. After it is enabled, the user's credentials (Google account and password) are required in order to reset the device, to allow a person other than the original user to use the device as intended.
A kill switch is not a new feature in the Android world, as Samsung has introduced it a while back, offering it with devices like Galaxy S5 and Galaxy Note 4. But, given that Google's Android is the foundation for virtually every other distribution used by mobile device vendors, the benefits of a kill switch will basically be available to the entire Android 5.0 Lollipop user base, no matter which manufacturer makes those devices.
But, as you can see, there are disadvantages to Google's implementation. The kill switch is not enabled by default, which means that users will have to know about it and manually activate it, in order to take advantage of it. For the less tech-savvy it is fair to assume that the kill switch will probably remain disabled until Google makes it active by default (presumably, it will happen right before or when the Californian law goes into effect, to allow vendors to sell mobile devices in the state).
Also, the kill switch in Android 5.0 Lollipop needs a passcode, which is likely required every single time the user wants to unlock the device. That can be a nuisance and I can see why many would not bother to set it up. Google should have forgone this requirement, while still designing Android 5.0 Lollipop to ask for the user's credentials to disable the kill switch, making the security feature easier to deal with.
The Android 5.0 Lollipop kill switch may not be perfect right now, but it sure is a welcome addition and a feature many users will benefit from. It should also drive mobile device theft down, as thieves will find it incredibly harder to sell stolen devices, which are clearly someone else's property, to their (unsuspecting) customers.