Dataslates are the latest additions to our hobby. Their counterpart in Warhammer Fantasy are called Battlescrolls, and what they do is add units or characters to their respective codices and armybooks. The wording is very carefully done for how these are to be used, and I for one appreciate that to avoid the confusion and discord on whether or not these releases are playable.
So lets take a look at the rules for Dataslates and how they interact with normal 40k and even Apocalypse.
These are not exact quotes, but are listed with the intention so that these rules can be understood for the community so that future releases are understood what they bring to the table.
Lets get the terminology down first that introduced with Be'lakor.
Dataslates: A Dataslate contains one or more datasheets.
Datasheets: Present either an army list entry or formation for the faction it is listed for. The army list entry can a single model, vehicle, or unit. A formation is a specific group of models or units that enable you to use special rules when you include them in your army.
Faction: Each datasheet lists what faction it is part of, and determines which codex the datasheet is part of for all rules purposes
Armies list Entries: Provides all teh information to field a single unit in games of 40k, and includes points and battlefield role. Can be used as part of any detachment that corresponds to the Faction listed.
Formations: These are two or more units that fight alongside one another in a particular way. When choosing an army, you can take a formations a special form of detachment, and can take any number of formations in your army, and each is considered a separate detachment.
It looks like December might just be full of these Dataslates, and we should be checking every day to see what is new. There are just lots of possibilities with the addition of these.