Jewish companion? How do you know we haven't already had one? OK, I can't spot any surnames with obvious Jewish ancestry, but that doesn't prove much, and if you can spot one line where a companion hints at a religious belief, you know Who better than I do (Victoria, maybe)... The only companion whose religious ancestry we do know anything about is probably Dodo, assuming she is genuinely descended from the Huguenaut (and therefore French Protestant) Anne Chaplette. It's just not relevant to bring it up - it's not as if the Doctor would care, he judges people on who they are, not what their ancestors are.