The Trust system works in FFXI because it was needed as the playerbase is little to non-existent while levelling now and doing story missions solo now make sense as most players ain't going to go back to content to help players complete if that content is no longer relevant to endgame.

The trust system isn't needed in FFXIV what so ever because the playerbase is very much alive at all levels due to roulette which already fixes the need for trust npcs.

However if the dev team are deciding to move away from roulette/tomestone system then trusts will be needed in order for new players to clear dungeons etc.