Personally, I wouldn't count on what they say even if you can go. That will mean nothing if when you go later to actually renew your visa they tell you something different. That is why I'm recommending keeping the 800,000 baht in a Thai bank account for at least 3 months prior to applying for the renewal.
I also still recommend renewing as far in advance of the expiration date as possible. It is my understanding that you can renew up to 1 month in advance. That way, if you do encounter problems you should have time to deal with it. Don't forget, even if you do renew a month in advance, the next expiration date will still be 1 year after the current expiration date.
As far as I know, those who no longer can get a proof-of-income affidavit, but can prove at least 65,000 baht per month coming in from a foreign source for a year or longer, are still supposed to be eligible for renewal. However, exactly what constitutes proof immigration will accept still is not entirely clear. I would imagine your bank passbook and letter from the bank will suffice, but does anyone know that yet? I'm planning to renew that way and will be bringing along additional evidence, such as a statement downloaded from my retirement income source. But just in case, I will also have the 800,000 baht and a letter from that bank ready. I'll dig that out if they reject my 65,000 baht per month proof.
I'm hoping they will accept the 65,000 baht per month. That will free up the 800,000 if something happens that necessitates spending it. But since we, at this point, have no idea what immigration will require a year later, I'm planning to just leave the 800,000 sitting there in the bank account, untouched.
That's part of the problem. There is just nothing we can rely on. If immigration allows the 65,000 baht with the evidence you provide this year, how do we know immigration won't yet again decide to change the requirements next year? The answer is we don't know. I wish immigration would put all the requirements in writing and give us some sort of binding guarantee that they won't change the requirements again.