Nexus Software Update Debate I need you end a debate me and my friend are having. He claims that the Nexus phones only have the capability of one software update in the sense that it'll only update to whatever is next after Lollipop and that's it while i claim that it'll update to every software update. Who's right. Thank You In Advance
Nexus devices will receive updates at least 18 months after their initial release. There are some minor releases 5.0.1 or 5.0.2, which are not distributed to every Nexus device because those releases may only fix bugs associated with specific devices.

Also, some devices will receive updates past the initial 18 months of its release. For example, the Nexus 4 was released in November 2012, but has still been receiving updates more than 2 years later.

It is also possible that a device will get no more than 18 months of updates. A famous example is the Galaxy Nexus, which included hardware made by Texas Instruments who moved away from phone processors. As a result, Google decided not to upgrade the device beyond Android 4.3, which means it only received 20 months of official updates. Despite this, it is still possible to upgrade to KitKat and Lollipop if you don't mind using community-created ROMs.

For an official resource directly from Google, they explain the Nexus update process as the following:


  Nexus 4, Nexus 5, Nexus 6, Nexus 7, Nexus 9, and Nexus 10 devices receive the latest version of Android directly from Google. Once an update is available, it can take up to two weeks for it to reach your device. Based on your carrier, it may take longer than two weeks after release to get an update.
  
  Nexus devices may not receive the latest version of Android if they fall outside of the update window, which is usually around 18 months after a device has been released.


Considering Google's recent emphasis on Android One, the system requirements for Android are likely to remain pretty lean for a while to accommodate the lower-end hardware Google seems eager to support. Since you tagged your question as "Nexus 6", it is unlikely you'll need to worry about Google upgrading your phone to the latest version of Android for a long time since the reasons of the past (lack of hardware capability) won't be an issue for you.