In the past there have been a few proposals for some of the languages of Southeast Asia on Stack Exchanges "Area 51", but none have made it to the beta stage. I'm not sure if any have made it to the commitment stage.
In the hopes that united numbers of people interested in all the languages of the area might be enough where it has turned out that the numbers interested in particular languages have not been, I have proposed a new SE site for all SE Asian languages:
Southeast Asian languages
Proposed Q&A site for language enthusiasts, learners, linguists, polyglots, and travelers interested in Burmese (Myanmar), Indonesian, Khmer (Cambodian), Lao (Laotian), Malay, Tagalog (Filipino), Thai, Vietnamese, minority languages of the region, and their scripts.
In case you haven't noticed it already and you are interested in any of these languages it would be great if you want to follow the proposal.
(By the way, there is also a Khmer Language proposal.)