The problem with unique content for the relics is that it either needs to be solo, or there needs to be an incentive for people to do it multiple times.

Imagine doing the first 3 primals now, if there were no tomes and no roulette bonus. You would form a group in PF, and beg people to help you out, or sit for hours in DF.

If they did put an incentive into rerunning the fights, then it would just be a new trial added in that required relic to unlock.

The solo route is a rough one, you would need a fight that was challenging and at the same time possible in 3-6 month old gear. And they would have to make one for each job.

I guess another route would be an open world spawn battle like the treasure maps that allows you to take in a party like the treasure maps. That's the only real option I see for it.