Why bother with the complication of a maglev? Railguns are quick, simple and easy. A gauss gun would give you more reliability, but isn't as efficient and let's face it, when throwing a few tonnes into space electrically you want efficiency!
Railguns have been demonstrated with muzzle velocities in the 15 kilometres per second upwards bracket. Wikipedia even reckons on 20kps!
Of course, to do this with a big mass would take a LOT of energy.
The two big engineering issues I see are
1) Power source: a rocket has several minutes and hundreds of kilometres to accelerate up to orbital velocity. Due to the size constraints of a ground-based solution, any means where the propulsion system is on the ground would have a fraction of a second to boost the projectile up to this speed. LOTS of power.
2) accelerative loadings. if you want to accelerate from 0-24000 mph in a fraction of a second, you will be applying a LOT of g's to the projectile. You tell an electronic engineer to design electronics to withstand thousands of g, and once he's slapped you for being delirious he'll tell you to naff off.
If the rail is 1km long, and you want to go from 0 up to 11km per second, accelerating at a constant rate, that will give you a time of 0.182 seconds, and an acceleration of about 6200g.
You also have other issues such as air density: rockets only give it real welly in the thinner air, but with our case you will be screaming through the thick sea-level atmosphere. You need to design your projectile to withstand extreme heat-cycling without failure. Probably simpler than designing an Ariane, but still hard.
Oh, and I haven't taken into account the air resistance: escape velocity doesn't account for air resistance! I'm not even going to attempt to calculate that, but I think a wet finger value would be to launch at 20-30km per second.
Then you would have some interesting difficulties with the Outer Space Treaty, you would have to prove the system could not be used for offensive purposes, nor would it be open to subversion to such purposes (so the guidance system could not be reprogrammable for instance, to miss the sun, swing round and hit the earth).
