A hidden mulligan already exists in the case of zero or seven 0 cost cards. It processes once, and if you get screwed again, too bad.
Having a full unconditional mulligan has proved to be a poor thing in games like Magic: the Gathering, resulting in some stupid decks like Dredge that can only exist because of the degenerate mulligan system. Other games like Android: netrunner somehow manage to do alright with it, though. I'd be against it in Elements, though; with so many starting hands often looking the same anyway, when you can have six copies of a card in only a 30 card deck, it would be pretty meaningless most of the time. It would probably buff fat control decks the most if a manual mulligan system did exist, though.