Amazon Web Services won't have a union because support for unionization among Amazon's developers is low. Amazon will split itself in two before this happens.

My prediction - warehouses that unionize will get split off into separate companies and be contracted out to by Amazon.com, the store. But they rely on Amazon.com for so much of their tech that they'll be beholden to them and have no leverage in negotiations. Warehouse workers will be even worse off than they are today.