The showcase feature is one of the oldest things about TMX. Its purpose was to showcase unknown authors and also to showcase community build maps.
But it came at a time when there wasn't as many ways to get your track known to the community. And it's always required a lot of work on the part of the crew to come up with new and different authors every week, and tracks that would be good enough to showcase.
I don't say whether the feature will return or not, but I think it's not as needed as it once was. There's far more ways now for people to promote their tracks themselves. And you can always showcase great tracks by other authors you find yourself via a front page blog entry.