TTVN:
This does sound more plausible, but I doubt it'll stay afloat since not many people watch SEA works. The point of wanting to add Vietnam to Mydramalist is to bring exposure to the country's media.
In Myanimelist, people are still adding Chinese animated works under the Japanese tag, and it all goes through, so idk...
Yeah, getting sustainable critical mass is difficult. Though this thread would be a steady source of new people :) But it might be better than nothing.
May as well try your idea to confirm.
Oh duh, check out Letterboxd. They have a fair bit of Thai drama in their database. Search is best by title so I can't see what they have for Vietnamese series. Socials are weak but you can make lists, follow others and keep of record of what you've seen.