The lawyers bringing this case are the same lawyers involved in the Shelby County case and basically the goal of this case is to reduce the number of minority districts in Texas or to dilute minority districts. Michael Li as a good explanation of this case http://txredistricting.org/post/83485633267/the-new-suit-over-the-texas-senate-map-an-explainer
The theory of this case has been litigated before and rejected.
In Lepak v. City of Irving, the lawyers in the Texas senate case - also backed by the Project for Fair Representation - represented Irving residents in arguing that the citys new single-member council district map was unconstitutional because it had been drawn using total population rather than CVAP.
Both the district court and the Fifth Circuit ruled against the Irving plaintiffs, citing the Fifth Circuits ruling in Chen v. City of Houston, which held that the question of whether to use total population or CVAP was a political question and thus not reviewable by courts.
The Irving plaintiffs sought to have the decision reviewed by the Supreme Court, but the high court declined last April to take the case.
However, the Texas senate case potentially represents another opportunity to have the Supreme Court take up the issue since any appeal would go directly to the Supreme Court as a matter of right.