Sony users have been waiting a long time for the successor to the Sony a7S II. But according to the most recent report from a source who actually used a prototype of the a7S III, the wait might actually be worth it. The report comes from Sony Alpha Rumors, who claims “a reliable source” told them Sony is planning to release an a7S II successor with a built-in fan and the ability to shoot 4K/120p video. Everyone is expecting 4K/60p,…