I'll chime in! :)
For JPMS, I think we should probably start some discussions around this, but there is still a lot of assumptions that are unsettled (like whether we can legally use a module name that starts with "javax"). Some of the issues to resolve is whether we want a single large module that encompasses the entire JAX-RS APIs or whether we want to be more fine-grained and allow users to pick and choose - i.e. just the client APIs, or everything-but-SSE, etc.
For NIO/Reactive, I think there is a lot of buzz around this, but I think the technology is still a bit premature. I'm still wrapping my head around the ideas of reactive, and others like the MicroProfile group are trying to incubate reactive concepts in a cloud-native environment. I suspect that as that group continues to make progress, open source implementations will start to form around it and then we can standardize on those implementations. I want to be cautious and not introduce unproven technology into a spec - and I think that was the argument Markus was making as well.
Hope this helps,
Andy