That's disappointing. My first read through of SSE didn't indicate the continued need for JS. What a sadly missed opportunity for HTTP.
I'm curious. This may seem like overkill and cause some other potential issues, but what about breaking the page up into a slew of [i]frames that update independently in order to keep context for the user and that would minimize the jarring experience that present browser implementations provide? (Wow, wouldn't it be nice if browsers did a differential render update for web pages or simply loaded in background and then faded in or loaded the update after the inbound page load was complete?)