Forgive my ignorance, but did AlphaGo not already establish that multiplayer games of the sort mentioned in the abstract are already essentially no longer a challenge for state of the art AI players?
"Overall, AI research has primarily placed emphasis on training of strong agents; we refer to this as the Policy Problem, which entails the search for super human-level AI performance. Despite this progress, the need for a task theory, a framework for taxonomizing, characterizing, and decomposing AI tasks has become increasingly important in recent years"