It was open to anyone years ago, but changed to this way as it gained attention from gov. It's very unlikely to see it going backward.
Anyways it feels weird being the only who pays cash. Many places cannot provide change for a 100 yuan note (20 usd).
I'm in the US and have colleagues who go to China on business trips. It's a huge pain. It's almost impossible and no good work around.
I can't transfer money to their wechat, and they money they have, they can't send. They cant even participate in grabbing red packets. A lot of Chinesw vendors accept wechat or alipay only, and if you use cash, people get pissed off.
It's a system unfriendly to foreigners. It's a shame because I prefer it due to its ubiquity but I can't see international adoption without radical changes by the paranoid Chinese government.