I think building a real lightsaber is possible. In france they have built a meter long plasma torch, if you contain the plasma in a magnetic field to shape the plasma into a rod like shape building a lightsaber could be done. the only problem is some how building a power source that could fit in the hilt. seeing as how you would need about 100,000 volts of power that part would be hard to do.
Not entirely impossible, just really hard to do.

Those who live by the sword, will die by the sword