Hello! First of all, thank you for enjoying the game so much, 1CCing hell mode with every character is a huge achievement that I'm sure very few players have ever reached.
I understand wanting new goals to aim for, but adding extreme difficulties or ultra-hard achievements would make 100% completion impossible for almost everyone, which is something I want to avoid.
That said, I'd encourage you to post a continuous streak run or self-imposed challenge videos if you'd like to showcase your skills!