I personally do not feel the need for a new element. The closest thing I would do would be 'Null,' which would be focused around my idea of Fused cost ideas, a psuedo-:rainbow element where cards, while being able to be paid for with any quanta type, must be paid with a singular element. Mechanically, they would have effects that differed depending on the element used to pay for it [if paid for with
, get +5/-5] and may be mark dependent [if paid for with quanta of your mark, heal 5 health] [if your mark is
, gain 5 health].
Alternatively, and this has been explored before with 'Blood' and similar type ideas, it would be a group dedicated to paying for cards with health instead of quanta. Mechanically, they would be cards that would deal double damage according to their costs [pay 20 health, deal 40 damage] or provide some positive effect over time [pay 10 health, put 5 purify counters on target].
However, both of these types can be fit into any of the existing elements.