Again, as mentioned before I do have plans for a Siam Split in the works. I've finally settled the details for the initial Sukhothai/Ayutthaya split; and am moving forwards with art. But in any case, my approach to the civs were as follows:
Sukhothai under Ramkhamhaeng now has a WLTKD + Science focused UA; the WLTKD part more accurately reflects the concept of "Father Governs Children", and the Science part shows us the thing he truly is famous for in Thailand: Inventing the Thai Alphabet (according to popular history anyways). I've had trouble coming up with a UU for Ramkhamhaeng as well; the best I could come up with being a Krabi Swordsman, which feels to me as ridiculous as a Shaolin Monk for China; so I've stuck with a Wat UB and Sala UI combo.
I have Ayutthaya under Naresuan, although the civ reflects the Kingdom of Ayutthaya overall as opposed to Naresuans reign (in fact the design would work better under Narai, but Naresuan's cooler). Siam's current UA goes here, with a small buff. The UB is a Floating Market (replacing the Harbor) and the UU is the Chang Suek (renamed Naresuan's Elephant). Essentially a CS Overlord and Trade civ.
Haven't figured out Siam/Thailand yet, but I can say it'll be under Chulalongkorn.
Sukhothai under Ramkhamhaeng now has a WLTKD + Science focused UA; the WLTKD part more accurately reflects the concept of "Father Governs Children", and the Science part shows us the thing he truly is famous for in Thailand: Inventing the Thai Alphabet (according to popular history anyways). I've had trouble coming up with a UU for Ramkhamhaeng as well; the best I could come up with being a Krabi Swordsman, which feels to me as ridiculous as a Shaolin Monk for China; so I've stuck with a Wat UB and Sala UI combo.
I have Ayutthaya under Naresuan, although the civ reflects the Kingdom of Ayutthaya overall as opposed to Naresuans reign (in fact the design would work better under Narai, but Naresuan's cooler). Siam's current UA goes here, with a small buff. The UB is a Floating Market (replacing the Harbor) and the UU is the Chang Suek (renamed Naresuan's Elephant). Essentially a CS Overlord and Trade civ.
Haven't figured out Siam/Thailand yet, but I can say it'll be under Chulalongkorn.
may be better suited as a UI as Established/Patronized Wat can be found in capital cities. If Sala would be an UI then should be unlock somewhere around Theology and have less yield but maybe increase with Education and other tech. I imagine it could be build on or near a road. You made a good design BTW. 
faith per each religious buildings and +1 
science per each scientific building present in the city working it. With CCCHP, it also grants +1 
culture per each government building present in the city.
