I start this with the caveat that my knowledge of Buddhism and Hinduism is very limited. With that said, here goes:
I read somewhere that a court in India ruled that Hinduism was really a cultural phenomenon and a way of life, not a religion. On its face, it is polytheistic, which obviously conflicts with my definition. It is also tied way too closely with Indian history and culture to be universal. Relative to my definition, it is a flop.
Buddhism is a tougher call. There are so many variants of Buddhism, some of which are metaphysically similar to Christianity, that it is difficult to analyze. The core of Buddhism, however, is the association of human life with misery and the attempt to mitigate it by overcoming desire. This method is both unchanging and universal, which meets my definition. If all of humanity succeeded in meeting the challenge of overcoming desire, however, it would cease to exist. In addition, much of the best of our culture can be found at the intersection of Desire Street and Frustration Avenue. Would we really want to give that up?