has it been a developmental dead end?

Nope, there are several companies & universities working on it.

W7x is the latest stellarator to come online, but there's a new Princeton University startup called Thea doing all the complex geometry and control problems of a stellarator in software.

It's a neat and elegant idea, engineering-wise. And no matter whose strategy works out, we all win in terms of understanding plasma physics, and possibly unlocking the secrets of the universe.