I don't think think Gridania needs to be "fixed", it's a very well done city. Black Shroud on the other hand could use some changing.
How about the obvious choice...?
They fix the game, people come back and clusterfuck Ul'Dah then decide to spread out cause of the lag.
Just remove the 3-4 stupid leves that everyone and their mom links/fails in the thanalan area. Problem solved.
I'd just like to add my two cents by saying that I think there are a lot of really good ideas being floated in this thread. I especially like the idea of city missions, intercity travel, city-specific dungeons, city-specific community activities, player housing with views of the city, and a re-worked Black Shroud. All of the suggestions in the OP are good, but these in particular would make me excited to spend time in Eorzea.
Community reps, if you get the chance you might want to forward the ideas in this thread to the development team. I know they want to hear constructive feedback that could improve the game, and there is a lot of it here. :)
Honestly i think the stories are following XI path of story telling . First few missions are kinda different then they all link for a while then they branch off seems like whats gonna happen again
Obviously it's hard to tell with the info we've got in hand but I have the feeling that companies will be the answer to most of the points that you proposed (intercity rivalry, city missions, associated dungeons and town defense). And the devs have stated that there will be a fame system. Airships, chocobos, we know they are coming.
So yeah I think future adjustments to the game will help spread people around, but I'm not sure that adding restrictions to current players habits is the good idea to provide this spread, like in some ideas that you posted.
Siefs boat idea wouldn't work simply due to LL is on the ocean and Grid is in the middle of a forest. Tbh It doesn't take much to travel from Grid to uldah then to the ferry to LL. Only time. And you rarely run into any agressive mobs. We need people to spread out their retainers due to the Ul'dah crashes. You guys want a hard core game yet are to lazy or whiney about sp/exp. Is there a need or reason to do the "best" sp/hr? Not really. Wait till there is content. And even still it is most of yaalls silly "rules" that "force" ppl to ONLY do leves in ul'dah. Personaly this is a community issue not the games. Most of your probs are in your head. Or ones you make up.