You can even make it so you don't unlock dungeons by doing it, but the remnants of the system would still grant you points and redeem it for rewards based on your licence. You can even go further and receive a bonus amount by queueing up as an adventure in need. The trials you have to go through will BE challenging so you can push as much as you can to complete it. No echo, ilvl sync, level sync to avoid any kind of cheesing.
After getting diamond, or within any rank, you can have several objectives, not only a single trial or quest. You can grab a bunch of challenges you need to complete before you can apply for the next rank. The possibilities are almost unlimited.
In my opinion this would solve several issues:
1) Will cut the DF queue times as there is another incentive for the roles in need to do it.
2) More people would strive to improve themselves to get the rewards.
3) Gives you both challenging solo content (Which this game is lacking) and more stuff to strive for.
4) An alternate way to get gear?
The system as I present it to you, in my opinion, has several potential uses. I took it from old school RPGs where you have a ranking and you need it to unlock content. Since this game loves to copy from WoW, I think that these challenges modes (Which is a variation of what I'm proposing) open more doors than anything.