I don't know what can honestly be done for Final Fantasy XIV at this point.

[Sebazy]

Job custom building would be meaningless. People will just figure out the optimal build and everyone will just use that. I'm pretty sure that's literally the reason this kind of thing doesn't exist in the game.

The solution to this is to simply make different content require different things so we don't all sit in the same groove. The flexibility of the job system offers so much but SE really fail to capitalise on it in the same manner that FFXI did.

*edit*

To clarify, I don't mean that X content requires you to queue as one job, whilst Y requires you to be on another.

Rather, raid tiers should be designed with more variation in what they demand from the different jobs within each role as to try and give multiple jobs an advantage over each other within fights of the same tier.

On paper, it's a great way to bust the monotony of people mindlessly following the meta, the downside is of course that the severe homogenisation that we have today makes this kind of difficult.