Online gaming: Real issues in virtual worlds (2015) [pdf]
pwc.es
pwc.es
Game economies do seem to be a strict superset of SaaS, so it's interesting to see what the state-of-the-art is for in-game revenue recognition since that will likely be a common issue as SaaS billing models become more sophisticated. E.g. usage-based billing is now becoming more prevalent (vs. simple per-seat billing).