At 1:1 there wouldn't be even close to enough height available to make even fairly small hills. Mountains would be entirely impossible. Also the render distance would be so short relative to the real world that you would never be able to see anything interesting anyway. For instance, I live in a valley in Washington. I can see Mt. Rainier from my house even though it is over 50 miles away. In a 1:1 version of earth in Minecraft, standing at the same relative location as my home, I wouldn't even be able to see the nearby low hills that surround the valley I live in, let alone the nearby mountains. It would suck.
I did a quick calculation. Assuming 9000 meters needed to fit Mt. Everest in, and allowing 1600 meters to put the oceans in (entirely skipping the true depth in many areas), 1:42 is the lowest ratio you could use. However, that would not be a very good idea because in terms of render distance, assuming you can render 20 chunks in any given direction, you would only be able to see things that are about 8.5 miles away. In many scenarios that would be entirely inadequate. For instance, you would have to be about 1/4 of the way up Mt. Rainier to see its peak. 1:128 would probably be a better choice both to make a realistic depiction, and to make the math easier... But you would still need a really large HDD to store it on.