That would be cool, certainly better than "CN" as China (PRC not Taiwan) has nothing to do with games in this category 
If we are to follow the established TLD rules, there is no TLD for SEA (and I would really not want to make things worse) ... but there is .ASIA.
I am thinking about it again... It would take more work to fix TLD on categories... since we have other problems. Having some categories like [CN] to take care of all of non-categorised Asian countries is not bad. We still have some categories using wrong TLD, such as [AS] (American Samoa) and [NA] (Nambia)... Not to mention that South African releases often end up in EU categories.
I think that the correct way to handle this would be to re-work the way we track releases, rather than trying to kludge it even more than it is.
I can't decide this on my own. Rather please post into this thread:
https://vgcollect.com/forum/index.php/topic,8361.0.htmlThe question being: "rename all [AS] and [CN] categories into [SEA]"
Note: it is not actually Style Guide related, AND us regular db admins can't rename categories. So if the motion is adopted, it may take some time before the changes are actually made.