It seems the rumor of a Thailand rumor isn't enough. Now Vulture is reporting that Paramount and Bay are planning to film Transformers 4 in China. The tone of the article suggests it is almost a done deal with the Thailand production simply being used as either as a negotiating tactic or additional shooting location.
There are several reasons being cite for the potential location choice. One is the growing box office numbers of China whose number of screens grows every year (35% revenue increase last year). Another reason is to curry favor with the Chinese government to get better treatment for Paramount films. Apparently the China government has been playing games with the release schedule either delaying movies significantly (Skyfall to next year) or suppressing box office totals by forcing moves to compete against each other (Amazing Spider-Man and The Dark Knight Rises released in same August weekend). Also China has instituted a quota for foreign films so I guess they figure an on location shoot will avoid them being impacted by it.
If you don't think the studios can be pushed around by China, it seems that would be wrong. Red Dawn was supposed to be about China invading the US but that was changed to North Korea when the country threatened to ban the movie. Portions of Iron Man 3 were filled in the country after an agreement with a state-owned media company there that will likely result in favored status for its planned release. The same company, DMG, is in talks with Paramount for Transformers 4. Paramount has not confirmed or denied the story, simply saying "the script to the movie is still being written. ...It is not a Chinese co-production,’ and that’s where things stand right now."
While for Paramount money is all that matters, there is an immense cost to filming overseas, especially a country like China. It wouldn't be a matter of bringing in the cast over there and then just taking advantage of local talent and equipment. Because of the technical demands of the film with visual effects and the like, along with Bay tending to use the same crew from film to film as they know his needs and demands, for all intents Paramount would have to ship hundreds of people to China with large volume of equipment. Every aspect of which would have to be supervised and constantly scrutinized by the Chinese government and most of which will probably be bitterly fought over by the country who would prefer they get paid by the studio to provide as much of the crew and equipment as possible. Never mind the risk that the crew would be taken going over there as foreign nationals do not have any rights in the country. Bay and the cast would be protected by their fame, the studio and the movie's insurance company. The crew itself would not enjoy the same protection.
I still maintain what I said before. Michael Bay takes pride in the economic boost that his movies provide in American areas and often chooses locations that would help depressed areas like Bethlehem, PA and Detroit, MI. I don't see him changing that stance. Could Transformers 4 film in China? Sure. Will the entire film be done there or even half of it? I doubt it. Especially once consider the tax breaks that many states provide Hollywood now. Besides, the studio would probably enjoy the same advantages of favored status by the Chinese government by simply letting 2nd unit film a few scenes there without having to deal with the bureaucratic nightmare (and potential risk) of filming an entire movie there.