As long as curves are gentle in relation to the speeds involved, they should
not be a problem as long as a maglev style suspension is used. The tube
would need some pretty good bracing to survive the side thrusts for anything
other than a really gentle curve, though. Obviously, rugged freight or bulk
materials could take much sharper curves than passengers!
One thing that would be a concern here is how much energy would be absorbed
by the levitation system. If you compress a levitating magnet using the
Meissner effect, you are adding energy to the system. There has to be a
limit to how much you can add for a given setup. Maybe it's just a matter of
proper design for a safety margin?
Chuck Kuecker