Wat Suthat and Giant Swing (Thailand)
Andaman Sea (Thailand)
Old Bangkok (Thailand)
Wat Phra That Phanom Temple (Thailand)
Not sure if this was picked up already... here a few more details on possible upcoming Thai Tentative List nominations (dated from May 2015):http://www.bangkokpost.com/print/530243/
Other potential sites we plan to add to the tentative list are Prince Naris's architecture, the cultural landscape of the Chao Phraya River, the Death Railway in Kanchanaburi, Si Thep Historical Park in Phetchabun, Wat Suthat Thepwararam and the Giant Swing in Bangkok, Wat Ratchanadda and its vicinity, archaeological and cultural Sites in Nan, Chiang Saen Historical Site in Chiang Rai and Wat Phra Pathom Chedi in Nakhon Pathom.
On the mysterious Chao Phraya River cultural landscape - this seems to be some scheme from the Thai Fine Arts Department to list central Bangkok as a WHS as a CL... as per the following link:http://www.asianews.network/content/chao-phraya-upgrades-looking-world-heritage-statu s-19807