The Android OS's current NFC code shuts the NFC hardware off entirely when the device is powering down or when the user turns off NFC, but a new code commit in the Android codebase points to some functionality that may change that. The code commit actually introduces version 1.1 of the NFC hardware abstraction layer, or HAL. The new version in the codebase adds in power-off use cases for NFC, as well as factory resets for the NFC hardware abstraction layer that doesn't require a factory reset of the entire device. It also adds in an automatic network reset event for the chip if there's an error. The resetting may just be for quick bug fixes since it will wipe the NFC chip's immediate data stash, but the power-off use case is a bit more interesting.
Presumably, this will allow some sort of low-power state for NFC along those lines to check for a user trying to initiate NFC functionality, such as mobile payments or Android Beam, while NFC is turned off. This could manifest as something like keeping NFC in a low-power state so that it can turn on automatically if a user forgets to turn it on before touching their phone to a payment terminal, a Bluetooth speaker, another phone, or other NFC devices, and that use case seems pretty likely. Something like a passive broadcast that announces the presence of an NFC-compatible device to other devices nearby is also possible. It could briefly power NFC on when close to other NFC devices, then turn it back off when they're no longer in range.
To clarify, a power-off use case is something like how Bluetooth and Wi-Fi are used for location when the user powers them off. They don't connect, and their scans are weaker, but as long as location services are enabled, those two chipsets never fully power down. The code commits say that NFC HAL should be able to differentiate between when a user wants NFC to be off, and when it's turned off because the device was turned off and the user never turned it back on. This change may bring similar functionality to the realm of NFC, but the commits don't go into detail about exactly how it will all work.