When is Thailand opening up?
It is already happening, bit by bit. The so-called Phuket sandbox started in July and has been met with some backlashes and some progress.
Beginning September people living in Thailand can start travel to any province without any restrictions. October the plan is to open up traveling for visitors from abroad but with some restrictions, not yet clear what. Probably minimum 3 days stay at an approved hotel/resort and minimum 7 days in the same area before can visit other provinces. Fully vaccinated, proof of testing being virus-free before leaving the home country, and probably 2 more tests during the first 7 days before traveling. Contact Thai Embassy in your country for detailed information.
Thailand opening up?
Beginning January 2022 Thailand hopefully will open up without restrictions, but that will depend on the development of the virus situation.
Inoculation of people living in Thailand is now in full swing and progressing very fast with more than 500.000 people inoculated every day. If that amount can be continued Thailand will reach 70-80% sometime in December and around 50-60% with two jabs. Thailand has close to 70 M inhabitants.