1.) The NBA players, pretty much unanimously, are now going to use all their ability to bring attention to this. Look at all the attention Kaepernick created, now the NBA is going to bring a lot of attention to voting and social justice as well.
2.) These arenas all exist in swing states.... They are going to create safe places to vote in downtown, urban areas in big cities. Arizona, Wisconsin, Pennsylvania, Florida, Ohio, Michigan. The NBA, NFL, MLB, etc all operate in these states. They are going to mobilize to get more people registered, and to get more people to vote. Every vote matters in a swing state.
3.) Apparently, some of these arenas are going to be taking votes from October 13th all the way to the election.
4.) The league, the players, the media, etc are going to be getting people to vote. The NFL, MLB, etc will possibly fall in line.
It's absolutely going to generate more voting. How much more, I don't know. But any increased voting is not good news for Republicans, especially in big cities.