Markus Karg typed a nice code prototype suggesting the use of java.util.Stream in scope of the possible support for SSE.
java.util.Stream is available in Java 8 and perhaps it won't map 1 to 1 to JAX-RS centric activities.
It would be very good for JAX-RS 2.1 API introduce a typed version of StreamingOutput, similar to java.util.Stream, such that it can be used
with or without SSE. Something like