Magic the Gathering House Rule - Face Down Cards are Colorless Lands

I've been cooking up a house rule for Magic the Gathering that would be fun in some of the modern General, Commander, EDH, and Highlander games. While following the 1 land per turn rule. You may place any card face down. This card counts toward your 1 land per turn. It can produce 1 colorless mana when tapped. That's it...haven't figured out what to call the rule maybe Face Down Lands, Colorless Land Rule, something like that. Maybe the Down Land rule.

This rule allows for some level of versatility when playing with large creatures that is typical of Commander games. Say you have 3 creature cards in hand, 4 land available, and would like to cast a creature spell for 5. Then, following the Down Land rule, you may put 1 of the creature cards from your hand face down with your land on the battlefield. Now you have the 5 mana necessary to cast a creature.

The new game mechanic of Morph, Megamorph, and Manifest got me thinking about it. It's just a way of balancing, speeding up, and otherwise making the game fun. I don't think I would play this rule as a blanket house rule, but would consider it under certain circumstances.

UPDATE: The rule is called Landfall. Not to be confused with a Fastbond House Rule which would allow players to play any number of lands on any turn.