I agree with the 'Nex Boss' thing, I belive this was a thing of the past and I would love to have it back into the game.
I disagree on the 52 wilderness frost dragons thing, but should have its owner lair in the wilderness.
I agree with the other ideas that you've suggest but having more completionist capes is getting.. a bit repetitive if you know what I'm getting at. Maybe add something else instead of another cape.. idk.
Good suggestions overall