There's actually a load of ideas Scorp has done in the past that aren't on this game to my knowledge, correct me though if I am wrong;
- Jibs/Jibuma with DarkFallz main boss; can't exactly remember but this has 3 stages I think, with ghosts in the room
- DarkArcher; I still think could be a fun boss somewhere to add, although Scorpian has previously said it's the nostalgia talking and wasn't actually that good
- The LOTR theme was always a fun one back in the day, an expansion could see us travel the Hobbit Series and go beneath the Misty Mountains to face the boss Great Goblin (a static or slow moving style boss), we move on through Mirkwood where we encounter a second boss, Bolg (a quick hard-hitting mobile boss) and eventually enter the Kingdom of Erebor and fight a new superbooss dragon, Smaug (RedDragon style boss).
Maybe some people see it as too cheesy to expand on that series now but it's always there.
This is going a bit far for today but gonna throw it out there anyhow, an Elven item set could be the next Elysian, upgraded to GreatElven, LightofEarendilsStar from currently dropping from Shelob could even become a useful in-game quest item..
I'm gonna have to take a breath and calm down now, got too excited thinking of that last idea.