Versions is a security feature for your content. Versions allow you to keep a copy of your Joomla articles every time you save a change.

The code for Versions has already been commited so it is certain to ship with Joomla 3.2 which is due in the next couple of months.

Read and see more here:
www.ostraining.com/blog/joomla/content-versions/

The obvious question now is, is this, and if so when is this, coming to K2? ;)

Implementation is possible as follows:

The versions are stored it a new database table called _ucm_history. UCM stands for Unified Content Model.

Over time, the goal of Joomla's developers is to unify the way that Joomla handles content whether it's articles, users or data from other extensions. This table should allow other extensions to also tap into Joomla's new versioning feature.

This feature is very useful!

I think it will be available for K2, according to the above quote, Joomla developers will make it available to other extensions to use the ucm_history table for versioning.