This is from the US embassy in Bangkok on their letter request form:

"According to verbal communication from the Royal Thai Government’s Immigration Bureau, non-Thai nationals can visit any Thai Immigration office to request a 60-day extension of stay. We have been told that there will be a charge for this. Thai Immigration will not require a letter from the Embassy as part of the extension request, so the U.S. Embassy and Consulate General Chiang Mai will no longer provide letters of support for Thai visa extensions. For more information about applying for Thai visa extensions, please visit or contact the Thai Immigration Bureau."

So maybe wait til the Immigration Bureau, the individual immigration offices, and the US embassy sync back up again. I don't doubt the embassy will offer letters again if they become necessary again.