I'd imagine that there's a great deal of prior work, research, and implementation detail on Maglev trains in Japan on this very issue. Not to say that you're not right, but that this test track is probably precisely what's needed for an initial test, since the other issues (commonly solved with expansion joints) are being actively tackled/solved by many different industries.
According to Wikipedia [1], the only 3 passenger service operational Maglev lines have lengths of 18.95 miles, 5.5 miles, and 3.8 miles, which are in China, Japan and South Korea respectively. That would make it seem like it is far from a "solved" issue.
