As the pillar is now, i would love it. I would upgrade this card instead of normal pillars, because it´s useful in every single mono deck, and doesn´t cost as much as upgrading Stone, Fire, Air, ... whatever. Since you only need to upgrade one sort of Pillars instead of 12.
That aside, just like pendulums, it will be used as a counter to earthquake in lots of mono-decks, which would mean an indirect nerf to earthquake. (I can´t really tell if this is good or bad...)
Further, it would make trio and quatro decks, even pento-decks (five colours) possible, because it gets the quanta of the cards you need right now... (But as I said, for rainbows 3 quanta per Quantum Tower would still be the better option.)
But I think the majestic tower shouldn´t be exactly the same as a normal tower. I think for the upgraded one the advantage "Activate when played" should be changed to something else. Maybe "Can´t be destroyed the turn after played" ? Just a feeling because a special tower should have a special effect. (And that way, for upgraded monos, it would be better to use their own coloured towers because of the extra quantum)
"Can´t be destroyed the turn after played" would be an temporary imortality like the one Seraph uses. Every time you would play a Majestic Tower, the opponent can´t destroy any of them in the next turn (cause they stack on the field, like normal pillars)
