Another idea: Ruin could just remove mana abilities, instead of all abilities. For most lands, that's the same thing. But it wouldn't effect Cathedral of War or Rath's Edge, for example.

Colorless lands that have ETB abilites will not be effected. Many lands with a one time ability won't really be effected either, assuming the ability is easy to do. That's because anyone who would have a problem with giving the land a drawback (i.e., Timmy) will do the beneficial thing first, even if it's not the most efficient way to do things.

Some lands could be made with a built in drawback that can be neutralized by Ruin. For example, a land that adds gains you life during your upkeep as long as you control 4 or fewer lands, but makes you lose life if you control 5 or more lands. It's a cute trick, but I wouldn't suggest including too many of these. Solving a drawback with another drawback gets into very dangerous territory.

As an aside, mechanics that return lands to your hand is very good here, both for the ETB lands, and for resetting Ruin. In fact, a cycle of cards like this seems appropriate:

Jagged Rocks
Land
When ~ enters the battlefield, you may return a Mountain you control to your hand. If you do, deal 2 damage to target creature.
­: Add to your mana pool.

Won't ruining a land get rid of any abilities it has, not just the ones that tap for colored mana? In that, lots of colorless utility lands still all get nerfed by ruin. I feel that would worse, since there's lower color density overall. Also, I worry that pushing colorlessness will name it too much like original Mirrodin and have the Blob problem.

Hmm. I'm a bit more optimistic than Dude, but I have to admit he has a point. Landfall makes a great mechanic because it asks for people to do something that they already wanted to do - play lands. Ruin is asking players to do something they don't want to do. If you put Zendikar packs next to Before Mana packs on a shelf and told people what the mechanics were for each set, you'd sell a lot more Zendikar.

That said, you could work this to your advantage. If there was any set where "Pay only colorless mana to cast this spell" was a viable option, this would be it. Also, if you could somehow find a way to Ruin a land by turning it into two 'deserts', then I think you'd be on to something. Maybe only occasionally... but enough so that people had a way to mitigate the drawback with a perk. I'd also look into creatures that operated as 'counter eaters'.

Alternatively, your set could just feature a lot of colorless lands with bonus abilities. You could even use the basic land slot to flood the set with odd lands. Instead of focusing on ruin as a mechanic, instead use flavor to evoke the same feeling. Personally, I think a mostly colorless set would be an interesting change of pace. And even if you still wanted to use ruin, colorless lands with enter the battlefield abilities and lands that say "When you ruin this land" might make Timmy smile again. Who cares if you're ruining a land if there is no drawback? Let players feel like they're cheating the system... people love that. ­

I think the reason ruin hadn't been used is because it's unfun. Too many people will screw themselves over by ruining too many of their colored sources and get locked out of the game. While this works flavorfully, game play must always take precedence to flavor. It won't be fun to play.