It's not a bad idea, but it's gimmicky just like Diablo 2.
Why do you think so much about each game is random? Areas are randomly generated, quests are randomly chosen, enemies randomly spawn (both type and location), and items are randomly dropped.
It's randomized because it's designed to be played over and over and over again. That's pretty much the definition of the end game.
Fine, then make the survival mode randomized. Have every wave set in a different randomly generated area. Each wave would have a set number of normal and super unique enemies, but their type and location would be random. Random quests could also spawn for optional challenges you could try, like 'find and light four beacons before time runs out' or 'get to the waypoint before time runs out.'
I'm not saying this should be THE end game, just one of many options in the end game. If D3 has a feature that makes it viable, fun and productive to run all 4 hell acts over and over again, that's great. But they could still add more modes for people who want to do more than that.
The D1 end game may have been fun, and the model may work in D3, but with all the gameplay innovations since D1 and D2, it would be a shame if they didn't try something new to give us more options.