So, I was talking with my guildies, who are all originally pen and paper players and most of whom were deeply in love with two things. The way you guys did Shavarath, and the Nine Hells in the Forgotten Realms. Obviously we have expanded to the Forgotten Realms; we have the Demonweb a terrifying always changing maze! But we do not have a hell. As we talked it over we came up with some interesting type concepts, some of which you may like some which you might not but I'll go through most of them anyway.
Nine hells means nine layers; this is by no means a small space to be building, we're talking expansion material, keep that in mind from a business perspective as much as anything. For at least the initial steps into the area and into such an expansion the following thoughts came along:
Epic spell books: we have a few epic spells from ED and epic feats but really what we want as casters is more variety in our spell book, if you've ever played pen and paper you'll remember the mischief one can get up to with a few cantrips - so these for fun (no need to just cater to end game players) but also a variety of more powerful spells and upgraded versions of spells we love.
A gripping story line: you guys aren't bad at this, really I liked Motu but Shadowfell is a bit "OOH there's bad guys, kill the bad guys, yay loot."
again this one pulls right off the Pnp shelf, you never enjoyed your pen and paper games when the story line was just around getting loot and leveling up. It was when you were a level two and stepping too loudly would wake up the dragon, it was when not defeating those bad guys meant you'd lose everything that you'd spent hours and hours creating and working for!That was when you enjoyed those games! And it was when the wizard summoned a bee in the jewelry merchants shop so that you could steel that fancy ruby to sell back to him later...
You get the picture, make us care about why we're doing it and make that why not "Loot" but "because that quest was really fun, like your Delirium quest chain, which is absolutely hilarious and a great load of fun even if a beholder manages to kill you every three minutes. The point being, if you take on something like the Nine Hells you can take on a large overreaching story line that can span many updates to come and that will be able to culminate in an EPIC finally where in you fell the great DEvil whomsoeverwhatshisnamethegreatandtyrannicalcousino fhorothbutnotreallycostheyrefromdifferentplanesand worldsandstuff (points to you if you can decipher that).
Mobs: You had it right on Ebberron guys, devils = endgame. Nobody wants to fight an orc and find out that he's harder to kill than the huge devil you stepped on in Chronoscope/Shroud/Tower of despair. I am aware scaling and difficulty levels exist but the principle is the same, you do not get to level 20+ on a pen and paper character only for your DM to whip out the orcs and the pirates and then for those pirates to give you more trouble than the giants, dragons, devils and liches you have been fighting all the way up until that point, it simply doesn't make sense. Give us newly textured different looking devils with new abilities personalities and what have you.
Hirelings: this was an idea from a buddy of mine and i quite like it. Devils are lawful right? So theoretically if a devil agrees to a contract s/he's quite likely to keep that contract until it is no longer beneficial to him/her. Point being, unless they're devout crazy people from some church that purges evil hirelings are unlikely to want to make it down into hell. This is where the Devils come in, Hirelings with "Evil type versions of destinies that need the tweak for role-playing purposes" that are in fact devils that have agreed to work for you, they'd follow commands more or less and generally behave like hirelings, you can have them be quite rude to players and if they die they can curse heavily(but creatively) at the player with even maybe some voice acting included.
Because this post has gone on long enough I'll finish with this; 9 hells three quests each with a raid per three layers and flagging raids for a big final showdown at the end.
Oh and friendly fire for certain spaces in quests so that a sorc can't just throw fireball aimlessly but has to think about his team.
Okay I think I'm done, sorry for the long winded post.