I don't know if the pillar bonus can be considered "passive".
I think passive abilities are the ones with symbols, like immortality, adrenaline, momentum or similar things...
Anyway, giving 2 abilities to the elementals will probably make them a lot more difficult to balance (both with each other and with other cards).
I think it's useless to make a super-uber-extra card, that cost 20 to play and so you will play only in one copy and almost allways without any strategy around it...
I want to make cards with new concepts, that work well only in mono decks and that encourage to build the entire deck around them...
So, even if immaterial air elementals or momentum earth elemental can be good, I think it's better to stick on a single, new, ability then mixing much of them... (In future, it's allways possible to make another card, even more improved, like "Primordials" that has the elemental ability and other things, but i think it's better to test them as they are before thinking about "adding more").