It seems balanced, but is it desirable?
It seems to me that the purpose of the pendulums was to push people more toward decks of fewer elements, rather than using most or all element rainbow decks, and it feels, at least to me, that it was a good step in that direction.
Adding a pendulum like this would, of course, produce much more of the quanta of a person's mark, but it would still be producing quanta for rainbows, not more concentrated decks.
If this was, indeed, the reason pendulums were introduced, I would have to say this is a bad idea.
That being said, I don't think its a reason to try to shoot down a balanced idea, since, if that were to be the case, it would just never be added to the game.