This is just a idea but something like this should be done to keep diablo fresh, new but also abit competitive.
I believe something like this game mode and other game modes should be created based on community suggestions and than drafted to the Diablo dev team.
I am sick of playing single player maps by myself for loot or with other players. blizzards new motto seems to be "think outside the box" which can be seen in new titles like "Hearth-Stone" Warcraft card game and the new MMO Titian.
To make Diablo fun, exciting and competitive the Diablo team needs to Step out side the box and stop following what they know.
I have heard speculation of a endless dungeon and other things. but imagine a game-mode that involved waves of monsters coming with bosses throughout completion of the waves. while this happens of course loot is dropping and elite mobs are included of course. And perhaps you are protecting for example Tyrial. to make things interesting say certain areas of the lanes contain "Shrines" which have auras that increase XP, Magic find or whatever to encourage you to kill monsters near them, but the closer you are to the portal the more mobs you will have to fight at once. Also treasure goblins can spawn aswell which would cause people to chase them :).
Of course the pvp is not direct pvp but there is another team which you are competing against and have ways of "killing them" like zapping their mana / rage to 0 and stays 0 for 10 seconds. or spawning a elite pack of random choice / affix behind them unexpectedly.
The winners are determined by which ever is unsuccessful of protecting there "wounded" hero.
We can expand on this but with what i have mentioned i hope i have shown you and blizzard a new path and ideas to think about.
Any thoughts about this Diablo Community?