Updates are not only for the latest and greatest phones, but they usually are. It's actually quite unusual to see a phone from a few years ago on a US carrier getting an update, but that's what's happening with the Samsung Galaxy Note II on Sprint. Rather, it will happen on January 6th.
Here's what you can expect in the update, version number L900VPUBNK2.
HD voice icon added
Google security patches (SSL, Towelroot, and TrustZone)
The firmware will still be based on Android 4.4.2, but it will have security patches for a few vulnerabilities including all those SSL issues from earlier this year and the Towelroot exploit. That will probably make rooting more difficult after the update. The HD Voice icon will presumably appear on the call screen to let you know when you're connected to someone using HD voice. Note, this is different than VoLTE on other carriers.
Samsung lists the deployment date as January 6th, 2015, so mashing the update button won't do any good just yet (or ever).