Facebook is a USA corporation but Facebook users are not only based in the USA. Well, its possible to go into gambling if they decide to, as they might not necessarily need any form of license from any government
Users are irrelevant in this matter. Since Facebook is a U.S. based public company, it needs to follow U.S. regulation. However, it can create a subsidiary company that focuses on an online gambling casino.
after all China has banned its citizen for a longtime from using Whatsapp chat and this has not stopped the growth of the application in any way..
WeChat is the main IM in China, read this
https://www.messengerpeople.com/global-messenger-usage-statistics/if 98 percent of their users are clamoring for coin gambling, i think they would be left with no choice than to approve
Even if 100% of the users demand gambling coin, the company still need to follow the regulation. Or they will be banned in the countries that forbid online gamble businesses (and gamble-related advertisements).