But the database (and accompanying tech platform) then gets cycled back into the hands of state and local parties, where it can be incredibly useful.

I'm not entirely sure that's the case. The DNC voterfile is compiled primarily from public record requests, and is as complete this cycle as it was in any other.

Narwhal and other OFA DBs may have supplemental information -- as do the "blue" vendors -- but that's separate from the voterfile, and I'm not sure its life-cycle is certain at this point.