They've actually now achieved over unity. The main sticking point left is the wall material. It needs to contain a hard vacuum. Unfortunately, the neutron flux transmutes the elements used. This has interesting results on the material stability. It's a solvable engineering problem however, though will likely be the limit on cycle times.

The current plan is building the first viable power station. Efficiency goes up with scale, so the current tech should make it viable. Multiple groups are building them right now, though it takes years to build one.