Who cares? Kushina got some screen time..FINALLY!
I see Kushina more of a prison for the Kyuubi than anything else. See how the Kyuubi was imprisoned inside Kushina's body? It couldn't move at all. It was practically crucified to a ball. Whereas with Naruto, the Kyuubi was merely caged, cuz it's a different seal. With Naruto, Minato made it so that the Kyuubi's chakra would always leak out, giving strength to Naruto. If Kushina was more of a container than a weapon, it would make sense to keep her jinchuuriki status a secret. She probably couldn't use the Kyuubi like other jinchuuriki use their bijuu.
I guess it was forced but it kinda makes sense.
Yondaime has already shown that he is capable of intertwining multiple seals.
Remember what the 1st 9 tails host said?
"The vessel of the 9 tails must be filled with love" -- or something to that effect.
Yondaime already showed up in a dire situation and gave Naruto the courage to push forward in the fight with Pain.
In another situation he needed something beyond courage -- he needed love and kindness to overpower the hatred of the 9-tails. The only way he could have done that was with the assistance of someone that could invoke those emotions.
That's where Kushina fits in.