As someone with Khmer family and who plays EU4 in SEA frequently, I'm loving the much needed attention this area is getting. I love the additional provinces everyone is getting, but especially Khmer. I do think moving Mon into the Burmese culture group is funny and Cham into the Viet-Khmer group is strange. The justification of language and culture not being equivalent, while true in whole, is not true for SEA. Language knowledge is what defined 'citizenship' in this area and time period. One generation may have originally been Khmer, moved to Siam, and two generations later were only speaking Thai. In the time and context, those grandchildren were Thai and no longer Khmer. However, if a different family continued to speak Khmer under Thai rule, they were still Khmer. Mon and Khmer are part of the same language group and, before being split by the Thai migrations, exhibited similar architectural techniques and patterns. There were also several Mon-Khmer client states. Similarly, Cham is a Malay language and the Cham had more in common culturally with their insular counterparts being a maritime trade civilization. The Cham and Khmer despised each other at the start of EU4 time period. Prior to EU4's time, both tried to conquer each other, and succeeded temporarily, but were both overthrown by local revolts due to each's nonacceptance of the other. As a game developer, I can see where these changes make for better map painting gameplay, but they take away from the complexities that are mainland SEA at the time that would make more intricate and focused gameplay early on when playing as Champ or Khmer.
Don't get me wrong, I love the attention this is getting. I'm super looking forward to the update! The inclusion of the Annamite Mts as impassible terrain and hill tribes between Khmer and Champa is beautiful! So is the idea of increased vassalization and super-cities mechanics, because that is how this region worked. I'd love to see some reciprocal obligation events for vassal and overlord. But, the cultural decisions being made here will limit the gameplay possibilities of historical plausibilities in this region.