Originally posted by Rooser
To answer the second question, I think the drawback will probably be that it will actually have a casting cost. If it was exactly Black Lotus, except it cost 3 colorless to put down, it would be balanced, but useful as a sort of Mana Storage Unit.
How would that be balanced? Grim Monolith only produced colorless mana and cost 1 less than this to put in play with a huge disadvantage of how to untap this and it was played extensively even before Voltaic Key.
If I'm not mistaken, WOTC has a policy against printing any artifact that can produce mana and has a 0 casting cost, so not even Lotus Petal should come back. Then again, WOTC does notoriously contradict itself. Still, my guess at to its drawback would be that it costs mana to put down.
Actually, they have a policy of being very careful about any one card that can generate more than a single point of mana. Gaea's Cradle and Tolarian Academy were more powerful than they expected (I'm not sure why, it was obvious to quite a few people before decks started showing up). Anything that produces more mana is considered "dangerous territory". Obviously, they feel it can be done and done well, but carefully and primarily in green.
So, if the lotus cost 2G, then maybe, but not 3 colorless.
The rumor I've heard about the Moxen is that the new Moxen will be just like the old (0 cc - tap for 1 mana of the given color), but will have the same drawback as Rock Jockey. In other words, you cannot play a Moxen if you have played a land this turn and the turn you play a Moxen, you cannot play a land.
This still has potential for abuse, but is nowhere near as dangerous. For the most part, it is a land, but if you draw 3 in your opening hand, you just play all 3 first turn and don't worry about a land. I suspect we will see quite a few decks running upwards of 20 of them (4 of each color) with only a minor color commitment.
As far as Lotus goes, I hope that they don't think that dropping that same restriction on Lotus will balance it.