This is what to me the game seems to be lacking the most.

A lot of the additional questing is just for vanity or pets.

Beyond relic improvement there's not much we can do to improve our characters.
When you hit a wall like Coil 4 or 5 there's no options for you to do to overcome those challenges until you've cleared it.

This is my personal opinion but I would like to see other maybe slower ways to obtain gear that would make clearing the bottleneck challenges more doable in a DF party. That way people could do something to work towards the goal of clearing harder content.

Maybe quests to earn melding slots for gear or earning echo points for a specific fight which would be consumed once the player clears it?

I know hc players hate these kinds of threads but I play a LOT 7 days a week and I've just reached a point where I can either keep doing the same fight attempts over and over or just play for vanity.