At this rate blizzard is going to hit the health cap 2.14bil before the end of the expansion. Heroic elegon has 1bil health (502), sha of fear has 1.6bil health (509) and we're going up to 540-550 (Ra-den probably drops "elite") or so with the next patch and then in 5.3 we're apparently getting item upgrade back to see another 8 item levels on top of that.
So I'm guessing we're going to see very few bosses with damage increasing mechanics, and the last tier will have a boss that dies, and comes back or heals. Next expansion blizzard is going to either have to do something clever or go back to their idea of stat reduction across the board. Should be interesting to see.