Since you can only have 3 in a fire team it would be great if you could join up with another fire team of your choice. That way you can have six friends in one server playing together. If its stays the same way as the beta, this won't be possible. This also is a way for bigger fire teams without actually increasing the fire team amount.
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The size of a fireteam isn't a problem, thus a solution to a non-problem doesn't garner any attention.