In a statement to Joystiq, a Microsoft representative said, "the 30 titles available for download at launch will carry either E or E10+ ratings; beyond launch we have no additional details to share at this time." Based on its statements, Microsoft's Game Room can only include titles that have been submitted to the ESRB in other forms (compilation discs, or through downloadable platforms). While it's possible for Microsoft to submit classic titles that have yet-to-be rated by the ESRB (such as titles released prior to the group's 1994 inception that have yet to receive a rating), the plan appears to focus solely on games already available in some capacity.
Microsoft said that because titles featured in the Game Room are "classic arcade and console titles" the company will be able to add any individual titles to the Game Room without submitting new releases to the ESRB for review -- provided they are currently rated E10+ or lower. While Microsoft says it currently has "no plans" to feature arcade titles rated Teen or Mature, the company confirmed it would be able to resubmit the Game Room application itself to the ESRB for a new rating, if higher-rated titles are considered for future release.