Is the Voting Rights Act still necessary?

That cuts to the heart of the challenge to the act presented in Shelby v Holder. Is there evidence that election laws passed in the state subject to pre-clearance because of past discriminatory acts, still discriminate based on race, meaning pre-clearance is still necessary?

Here's an argument that there are political incentives for majorities in the states to discriminate, regardless of whether it is done due to racial animosity. The argument reminds me of points made in 2305 about factions in Federalist #10:

. . . regardless of whether white political leaders in these states hold racist views, they have substantial political incentives for engaging in actions to suppress or dilute the minority vote. 

In addition to a history of racial discrimination, the states covered by Section 5 are characterized by an exceptionally high degree of racial polarization in voting up to the present day. Whites and nonwhites in these states are deeply divided in their political preferences, resulting in a two-party system in which one party depends overwhelmingly on votes from whites and the other party depends overwhelmingly on votes from African Americans and other nonwhites. This racial polarization continues to provide a powerful incentive for leaders of the party that depends overwhelmingly on white votes to suppress or dilute the votes of African Americans and other minorities.

Party identification is more polarized along racial lines in states covered under Section 5 than those that are not:

We can assume that minority votes will be suppressed in these states because it makes electoral sense to do so.