To me it seems like it was only done to bring Sasuke and Naruto closer through similarities and what not, both being one of the last survivors of their destroyed clans. It was also done to have Naruto be relevant to the whole Uchiha-Senju destiny crap, since we all know you must be from that lineage to be relevant. Not to mention Kishimoto was never planning on exploring Kushina's character or even writing about it until after he became a parent.
Also, he said in an interview that he wasn't sure/.didn't know what relevance the spiral on Naruto's clothing had, only that he was trying to find a way to put it into the story, showing a clear sign that he hadn't thought up of the Uzumaki clan until much later on into the story. Contrast this with Oda, who, when asked about the D in Luffy's name, said that readers should simply read it as such until he revealed what it's meaning was.
