I shared a concept of my personal "fantasy" endgame in this thread; http://us.battle.net/d3/en/forum/topic/10787138807
Obviously, implementing a feature of that scope in time for RoS launch is unrealistic based on limited time and resources, but the underlying theme behind the concept doubles as my feedback re: endgame functionality.
To elaborate, I think competitive elements are the answer to further developing the endgame, and to that extent I think the prospect of ladders looks very promising. I feel it can be pushed even further though, to give the playerbase more competitive options outside of simply "grind Paragon the fastest".
Some of the more simplistic competitive implementations could include rankings for Massacres, Mighty Blows and Boss Time Trials. Measurement of these elements already exists in-game to an extent, so it would just*
involve applying existing client data to a ranking system.* Still a hefty undertaking no doubt.
All in all, the endgame of Diablo has and always will be about the loot-hunt, but that doesn't mean it can't operate as a greater means to an end (that isn't solely farming efficiency). I firmly believe that interesting competitive elements would compliment that core aspect of the game, even moreso if those competitive elements encourage alternative gearing, builds and playstyles that the player wouldn't consider otherwise. "Endgame for Everyone"