It's interesting that someone brought this up, since I have a somewhat similar thought and have been considering making a new post for a couple weeks. I haven't done that because: 1) it's rather close to the DE's release, 2) I'm not sure if there are many players who feel the same, and 3) I'm aware that this idea caters to a small group of hardcore players.
Basically, when thinking about the game in general, I feel "there's not enough EPIC BOSSES!". I can recall a few encounters that stand out as challenging, but there's only one that stands out as truly an "epic boss encounter". Not just one magister with unique name among a bunch of other magisters. What I have in mind is something close to Adramahlihk's level. Something that stands out even among all the bizarre encounters throughout the game. Something that has unique, *non-standardized* abilities and strengths and weaknesses, and requires tactics more specific than essentially whatever you do in almost every other fight, to beat. Something that even the strongest party needs a carefully thought-out plan to survive.
The one dragon you run into during your roaming days is a good guy you're not even supposed to fight, and he's a low-level character anyway. I always thought that's such a shame, even though in this game's settings dragons are perhaps not as iconic as in the D&D settings.
Also, one problem here is that, even against the toughest enemies you run into during your playthrough, you do essentially the same thing to beat: burn through their armor, then perma-cc, until they're dead. This really takes away the uniqueness of enemies that have unique designs and are supposed to stand out.
It doesn't have to be an entire string of quests just to lead to the optional boss, either. It could be something as simple as a lever hidden in some existing dungeon that magically teleports your team to one extra optional room guarded by an unusually strong boss.
So while what I have in mind is not one specific boss like the OP does, but it would certainly be awesome if the DE comes with at least one extra optional epic boss that is both memorable and *actually* challenging.
