So far it's looking good for me as well. Immigration pointed out when asked that while it's possible to do the retirement extension on a non-b, they suggest the paperwork involved was prohibitive (much more than just a termination letter, apparently), and it would be easier overall to just change my visa type from Non-B to Non-O, which would only require the Termination Letter from my job as the "reason" for the change request, and no other work related documents. To me a Non-O or a Non-B matters not, to be honest, as long as my retirement extension gets done without me heading to Lao. Easy is what I'm going for here so if the visa change from B to O, instead of a retirement extension, is what's easier for them then I guess that would make it easier for me too.
In any case, if anyone reads. Contrary to popular belief, yes, changing from a Non-B to a Non-O without leaving the country is possible, and getting a retirement extension for a Non-B is also possible. Just make sure you contact immigration for the specific documents they in particular require. (My location document requirements are extensive.)