This post, while applicable to Softcore will more add more to the Hardcore endgame experience than softcore with the comparison of death penalties and the ability to push on the higher difficulties.
Walking through the current Hardcore Endgame process we find ourselves as fresh lvl 60. The priority at this point is gearing up in MP0 to the point where we can either survive a DC and continue on or one shot everything possible so nothing can get close. At this point you bump up the difficulty to MP1 in order to farm better mob densities. Besides farming Hellfire Rings there is no reason to bump up the Monster Power.
In Reaper of Souls the goal is to make Adventure Mode the most productive way to farm XP and Loot. In Softcore the gear we acquire will allow for aggressive gameplay assisting players to push up the difficulty for additional challenges and whatever minor rewards are added to playing in higher difficulties. While the introduction of BoA gear will level the playing field more between HC and SC players you still won't see HC players being able to play at the highest difficulties.
For the hardcore players our characters survival is number 1. Unless a sense of progression exists for our character at the higher difficulties most Hardcore players won't venture out of there comfort zone. The best path will be grinding content we overgear to in order gain paragon levels. With the addition of the BoA system an interesting opportunity arises for players to be able to find unique items that can only be found in higher difficulties. This should not be in the form of gear or patterns (as we learned with the patterns from bosses that came in 1.0.8) once these are found no more reason will exist to play in the harder difficulty.
These items should act as a way to augment our current gear making the climb to higher difficulties possible and making our characters stronger (offensively, defensively, increased self healing). This is an elaboration something that currently exists in the game that will be broken with the removal of the AH "gems".
A new Bind on Character metagame: gems.
Helm - Gems = %Increases (Experience, Defensive, Healing)
Armor - Gems = Raw Stats ( Vit, Str, Dex, Int, Armor, All Res, HP Regen, Life on Hit, etc...)
Weapons - Gems = Offensive Stats (Crit Chance, Attack Speed, Crit Hit Damage, CD Reduction, etc..)
RoS Difficulties: Normal, Hard, Expert, Master, and Torment I-V.
At level 70:
Normal Mode should drop the current Marquise level Gems including new gems.
Hard should have a chance to drop +1 level gems
Expert should have a chance to drop +2 level gems
Master should have a chance to drop +3 level gems
Torment 1 should have a chance to drop +4 level gems
Beyond Torment 1 a system of risk vs reward at each level of gem should be included.
A Torment 2 (+5 Gem) has an x% chance to combine with a level 4 gem successfully.
A Torment 3 (+6 Gem) has an x% chance to combine with a level 5 gem successfully but a (100%-x%) chance to reduce the gem to level 4.
A Torment 4 (+7 Gem) has an x% chance to combine with a level 6 gem successfully but a (100%-x%) chance to reduce the gem to level 4.
A Torment 5 (+8 Gem) has an x% chance to combine with a level 7 gem successfully but a (100%-x%) chance to reduce the gem to level 4.
All difficulties can drop gems that are at a lower than the current level. Higher level gems have increasingly lower drop rate.
Lvl 70 gems require level 70 to use,
Gems are destroyed when removed from gear.
Gem mouseover will show increase increase or decrease in DPS/EHP/Healing when gem is dragged over current gem
Please list your ideas for new gem types in the following format
(Helm, Armor, Weapon) - Effect/Stat