Can I extend my non-immigrant type O spouse visa for one year after a 60-day extension if I haven't met the 400k financial requirement yet?

Yes, it is possible to get a one-year extension on a non-immigrant type O spouse visa even after being granted a 60-day extension. If you have not yet met the financial requirement of having 400,000 THB in a Thai bank account, you can seek an additional extension to allow the necessary time for the funds to meet the requirement. This situation is not uncommon, as immigration offices often suggest such extensions to help applicants fulfill the financial stipulations.