@khanwashere: Probably add the maps in over time, like all MP franchises do.
Sometimes it's too much repetition (Gears series), sometimes it's magical (Titanfall 2 reimagining of the original's amazing "Rise" map, free next week).
@Atzenkiller: Preorders generate very specific statistics, which publishers ABSOLUTELY rely upon for numerous purposes.
The beta gameplay is so short that it's not worth giving them that additional undeserved stat (since they'll report on preorders, not preorders canceled).
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