Back when you first get your Traverser Stones and whenever you try to get more, Joacchim mentions that spending prolonged periods inside Abyssea could have detrimental effects on you, but no such effect is really present.

People want to live in Abyssea and I am beginning to feel that the threatened "detrimental effects of prolonged exposure" need to be implemented to Abyssea to get people out of those areas and back into the rest of the world.

I personally would like to see more consequences to spending time in Abyssea. Maybe something like for every hour beyond the first two you spend inside Abyssea, you receive a penalty to your character (A reduction in stats, possible reversal of Atma effects) that will last until you leave Abyssea for a period of time equal to the amount of time you were there.