Well, as usual there are variable answers to numerous issues, depending on what office you are dealing with. One of my information sources was a moderation of the Thai Visa website. I presume he knew what he was talking about. Obviously, things may have changed. I will be soon testing the waters re the future of my extension - to continues as retirement or change to marriage.
So you were short 40K BHT in some months, but made it up later? I was advised by several "experts" a few months ago that for a marriage visa the deposits could be variable throughout the year as long as they averaged 40K or more total for the year. Such a situation is apparently not allowed for a retirement visa.
Yes visa approval issues, as well as her personal adaptability to USA, such as English proficiency, ability or interest in working, etc, etc. The list is long.
6 months a crack is maybe OK, if he can still have eligibility for UK NHS, if he were to need it. Otherwise, if he has adequate funds for healthcare here, then it would be good for long-term. Best of luck.
Don't wait up for any solution or resolution to this. I think landlords are going to get fed up with this faster than the expats and, as is already happening, will refuse to rent to foreigners. I would be surprised to see any loosening of the "rules" here. Other shoes are waiting to drop, such as insurance requirements. At least I am fortunate in one regard. My wife is my "landlady" and she said she would tolerate renting to a foreigner, IE only one who met all her "specifications".