Right now there is a bit of an unbalance in the way pledged work. You get the same reward for doing City of Ash hardmode as you do all three hardmodes in stone garden? Poor Maj has wasaaay more dungeons to sort through than the other 2 do, and more every year!
I propose adding a 4th quest giver, who exclusively handles the DLC dungeons with 3 hardmodes, and then shake it up a little.
Normal pledges: 1 key
Vet: 2 keys
Vet hardmode: 3 keys
Vet 3 hardmodes: 5 keys
This will encourage people to try out hardmode content that might otherwise prove to be.... daunting, and it honestly makes it more likely for people to do the DLC pledges period. I honestly don't remember the last time I did the DLC pledge, because they are downright tedious. 99% of the time.