It's certainly an odd time for Thai Immigration to infuriate a large number of expats living in the country. You'd think Thailand would be doing all it could to keep people here, or at least to entice tourists to visit. By the new rules, according to Thai Visa, who always get these updates before anyone else, any person entering Thailand through a land border will receive only a 15-day permit to stay.
This means that if you do a visa run over land, you can only extend your trip for 15 days. What is unclear is how, if at all, this affects the 90-out-of-180 rule. According to that regulation, visitors without alternative visas are only permitted to stay in Thailand for 90 days in a period of 180 days. If this rule isn't changing, then it just means that some people will have to do twice as many border runs as before.
Travelers arriving by plane still get 30 days on arrival.