It's unrealistic to the point of Thailand not having immunized the vast part of it's own population by then and likely not before sometime in mid 2022 as things are going right now.

To have an estimate, while the rest of the world is starting to provide vaccines to their population the Bangkok Post wrote this week that Thailand won't get any before March/April of this year. That should give you an impression of the schedule we're talking about here.

If you expect visa free entry without COE certificate and without quarantine I wouldn't expect much this year. Even vaccinated individuals can still carry the virus and there won't be much movement until Thailand deems itself largely immune.