Is Nginx next? I suppose that it's open source nature mitigates the risks of an important software infrastructure piece being developed in a country that might not always be friendly to us.
Nginx isn't a security company and doesn't make client-side software, so probably not. (Of course, theoretically nginx could be backdoored to give valuable information to intelligence agencies, but it's harder due to the fact it's open source, and even if it was closed source the escalation in response to banning nginx could start a new Cold War. Imagine the US and Russia mutually banning use of any of the other side's software and actually trying to implement it.)
It's entirely possible. I know of a certain open-source application that was banned from an entire component of DHS, specifically because the developer is Russian.