This is an old idea I had when pendulums were introduced, and since then I haven't played the game so much. I doubt it's a very original idea but I haven't been able to find it in the forums including the thread for new ways to generate quantums in the card ideas section.
Anyway, the idea is very simple: a Mark of Other that generates 3 random quanta per turn (equivalent to a quantum pillar). I think this would synergize very well with pendulums which can then allow for new types of decks based on "lopsided" rainbows; rainbows which are predominantly focused on one particular element, even though both the mark and pendulums (on every other turn) generates some random quanta as well.
For example, one might choose this Mark of Other combined with Light Pendulums to create a deck that's predominantly a light deck but allows crusaders to effectively use weapons abilities and to allow Pegasus to do the occasional dive.
Of course, as with any other change like this, there is a potential for new type of OP decks to be created. Still the idea is very interesting, I think, particular when considering how this would interact with pendulums.
If we look at elements like water, chrysaora needs death for poison, toadfish needs air for inflate, mindflayer needs aether for lobotomize, steam machine needs fire to gain charges, trident needs earth for tsunami.. already a lot of deck ideas making use of various water cards will have no choice but to become duo/trio/rainbow decks... But this Mark of Other, combined with water pendulums, could allow one to make use of a lot of water elements while still predominantly generating water quanta.