For several years now I've used an income verification affidavit from the US Embassy when obtaining by annual retirement visa extension at the Surin Immigration Office. They also have required copies of bank entries into my Bangkok Bank direct deposit account for one year. I would venture that with the end of income verification letters they will require a letter from my bank as further proof of income.
I know several guys who have obtained visa extension in Bangkok and Ayutthaya using only the Embassy letter without any other forms of verification. This loophole will certainly be coming to an end.