This may not be relevant, but I'll mention it anyway. I had a similar experience with an annual multi- entry Non-O many years ago. Due to work commitment, I needed to renew this visa at KL Embassy early. There was about 3 weeks remaining on the existing visa. The Officer was not happy about it but they did cancel the existing visa and reissue the new annual visa.
Recently reentered at Mukdahan Lao border checkpoint. They have their own homemade version of the TM6. Small slip that asks for arrival vehicle ID, address of place you will be staying in Thailand, and phone number. I think that is it. They keep the slip, nothing goes in the passport. They understand the need for the TM6 so take the initiative to continue collecting this information.
You may want to look into the Thai Privilege visa program. Formerly known as Elite visa. They offer multi-year packages. They are a little on the expensive side, but it sounds like you have made the commitment and are in a financial position that would enable this option. This is a relatively stress free service. Google them to find out more information.
There are some American Expat FB groups in Thailand that may cover the passport renewal process for Americans. The Embassy website also gives detailed procedure for renewal. A little confusing because it is detailed. I think the FB groups can give you a good idea how long it may take for renewal.
I think for countries bordering Thailand, the appointment system was a good option and more practical than e-visa. Or they could offer both options. I think the biggest issue with e-visa is approval time. For instance if someone is going to a neighboring country to apply for a Non-B visa for a new job placement. I don't think the employer will be impressed with the time required for visa issuance for there new staff. In time the authorities may re-evaluate their decision.
Part of the e-visa application process is to show proof of your location. People are saying it's best to use entry stamp or possibly hotel payment invoice. It may have something to do with network security. I'm sure there is a valid reason for not accepting online payments.
When you receive the approval email for the e-visa, how long is this approval valid for? Are you able to spend a full 60 day plus 30 day extension visa exempt inside Thailand before you must leave Thailand to activate your visa? Thanks!