Eh, screw it. Let's spend some time with the measuring tool in Google Earth. All numbers are approximate and may be rounded off, but always rounded up to account to measuring errors.
Idle plot in Efteling: Approx. 120x250 meters*
Standard football field: 90x110 meters
Joris en de Draak: 205x135 meters
Baron 1898: 180x50 meters
Python: 140x50 meters
The east lake in Efteling: 300x150 meters
Taron: 130x60 meters**
Kanonen: 100x30 meters
Balder: 130x65 meters
Helix: 300x120 meters
Standard Vekoma Boomerang***: 85x35 meters
Speed Monster: 250x50 meters
Den Aller Minste: 8x18 meters
Stealth: 150x40 meters
Swarm: 200x90 meters
Colossus: 200x40 meters
Nemesis Inferno: 100x150 meters
Formula Rossa: 560x190 meters
Flying Aces: 180x180 meters
Storm Runner: 180x150 meters
Skyrush: 200x200 meters
Maverick: 200x200 meters
Top Thrill Dragster: 350x40 meters
Mean Streak: 270x120 meters
Duelling Dragons site****: 190x180 meters
Beast (Kings Island): 610x330 meters
Steel Dragon 2000: 750x200 meters
Okay, at the end there I just tried to find coasters with really large footprints, but you get the idea. Most coasters out there are actually vastly smaller than the plot Efteling has set aside for development here. Of course, it'd be hopelessly optimistic to assume that they want to use all of it for one coaster, but they wouldn't really have to unless they're planning a Giga or something with multiple launches in different directions. You could fit pretty awesome things in a third of the space too.
*I have no idea how long the plot is, and the terrain gives no hint either, but it's 120 meters wide and stated to be 3 hectares (30,000 m2) in area, which makes it a matter of simple calculation.
**Still under construction in the Google Earth pictures, so the width is very approximate. The whole construction site is 80 meters or so wide.
***Sampled from Cobra at Walibi Belgium
****Because this question will undoubtedly spring up in that discussion as well.