So... I do like the increased level of difficulty. That said... I was still able to solo a bunch of content on my Cleric.
My main concern is what you plan to offer as a reward for running this mode. My hope is that there will be NO power creep... however if ANY power creep is introduced it is in the form of short term effect consumables. Please do not have us level up weapons or gear or gain new abilities or really gain any form of power because we ran REAPER mode. A few ideas on how to utilize the XP (other than consumables) would be to spend it on cosmetics. -OR- It would be extraordinarily awesome if you created a leaderboard which displayed a top 10 (3, 5?) list of the players who had earned the most "reaper xp" per quest. Maybe even have an overall leaderboard which shows total reaper xp earned?
My second concern relates to Casual/Normal/Hard/Elite... which need to be tweaked. The gap between Hard and Elite is too steep... but not because ELITE it too tough... but because hard is too easy. Hard should be more difficult and Elite should be bumped up a bit.
There are already people completing Reaper 10 Skulls without any issues. That alone should be enough to tell you we do not need more power creep. The challenge is welcome... the reward should be something other than yet another boost to character power. Not to mention that if additional power creep is introduced via reaper mode... it will increase the grind EVEN more than the HPL/IPL/EPL/GEAR grind... making even more difficult for newer players to "catch up" and adding to the already existing discouraging aspects of trying to keep up with multiple toons.