This is really "just" a suggested experiment to test whether or not an idea is possible, not a fully fledged propulsion concept. The idea is to place two thin and very smooth plates very close to each other, at a distance where the Casimir effect takes place, but with a twist. The twist is to temporarily magnetize the plates at exactly the moment they are pulled together by the Casimir effect, causing the magnetic field to act in the same direction as but much stronger than the Casimir effect.
The test is not about measuring the Casimir effect per say, which would probably be impossible due to the much stronger magnetic field. What the test is about is to see if the presence of a Casimir effect (even if it cannot be measured itself) causes another, stronger force (that alone would not generate a negative pressure effect) to massively amplify the otherwise very weak negative pressure of the Casimir effect. The test can be practically done by having a laser beam pass close to the set-up and see if its direction is changed.
If this experiment shows that such an amplified negative pressure effect exists, it opens up a practical way to produce the large amounts of negative pressure needed for exotic matter-demanding breakthrough propulsion concepts. Of course a complete spacecraft would need much more than a single pair of tiny plates but let's begin with testing the theory before scaling up to application, okay?