Okay, so we have 4 difficulties already and that's splitting groups as it is but for those who have many past lives, tomes, gear and game knowledge elite is no longer challenge enough and enhancements and changes to random loot have buffed up characters along the way too.

So how about this for a solution:

Remove casual.
Leave Normal, Hard, Elite, add new difficulty call it Mythic/Legendary/Buttstomping Difficulty of Doom
Leave favor as is and new highest difficulty adds only 1 or 2 favor to elite favor. (I'll discuss why later.)
Devs could add special loot that only drops on highest difficulty but in favor of less work it could be sufficient if the drop rate of named items in this highest difficulty was just higher than usual, whatever that may be.
Increase XP for highest difficulty at the same rate that it increases from Normal to Hard to Elite.
Bravery Bonus stays the same as if this were an elite completion.
Absolutely zero scaling on Doom.
Finally, you can not enter DOOM over level. That's right, you want that extra drop chance at some named item? It's your DOOM!

In the new difficulty all mobs are champions including Boss. Champions on Buttstomping Difficulty of Doom get extra buff or two (beyond what champions already get on elite) and a random selection of two to five minute spell buffs they can cast on themselves or allies like deathward, stalwart pact, displacement, stoneskin, etc.

What this solves? For those of us who haven't ground out past lives, uber raid gear, tomes etc, and were enjoying the game just fine pre-champions we can go back to playing the game (albeit with the champions as they currently are) and finish doing those things at roughly the same difficulty those who've already done so had and still get our bank and inventory favor with only a little more trouble than in previous years whilst those who need "challenge" for adrenaline can get it and those who claim to want "challenge" but really want better rewards can get a little of this too and can then stop trying to make the game harder overall.

Keeping the increase to favor low, rewards those who do the highest difficulty by giving them a margin for acquiring the +5 favor tome while at the same time not making that too easy. Keeping the increase to xp inline with the other difficulties and not increasing bravery bonus beyond its current implementation has the dual purpose of not increasing leveling speed exponentially and not exacerbating the current issues with bravery bonus streaks and grouping. Additionally, having Doom count as elite reduces work for devs.

The only thing this doesn't solve is the issue for people who want "challenge" for bragging rights.

Do I think this will ever be done? Not likely, its probably too much work and investment for what I think (just my opinion here) is probably a small portion of the playerbase who want difficulty increased across the board after they've done alot to decrease their own personal challenge (ie ground past lives, tomes, gear). Don't get me wrong, I don't blame the players, character improvement is the goal but some of these things like past life feats and tomes and the whole TR process are unique to DDO and I think some players may loose sight of that and how difficulty affects first lifers with little twink gear.

So really this "Suggestion" is more in the way of a daydream.