
I too doubt that it is just a form of MS.
I think it is stated that the Uzumaki's were destroyed in war because they were too much of a potential threat with their awesome sealing techs.
But yes, it would be awesome to find out about Uzumaki and Senju relation. Could be like this:
The Uzumaki are actually descendants from the So6P and the younger son might have made a clan with the symbol of the oldest son because he respected him. And because the Senju are descendants from the younger son, they are related to the Uzumaki.