I know the word FFXI is a taboo here, but as the developers have mentioned multiple times, they want to work in that games direction, as lets face it, it was freakin awesome.
I doubt there is a single person playing XIV that hasn't invested considerable time into Vana'diel's incredible storylines, gameplay, events, NM's, HNM's, Assault, Beseiged, Salvage, Dynamis and all the other wonderful bits that made up one fantabulous game.
In the same respect, you would ally to a nation in that game, and be locked to that nations storyline until you completed it. Understand that CHANGING NATIONS WAS NOT POSSIBLE UNTIL A VERY LONG TIME AFTER THE GAME WAS RELEASED and iirc it was mentioned often that they didn't want people to use the nations as a flavor of the month system, instead wanting people to work for and protect their chosen home town.
With that said, I would imagine once we see the end of the grand company story ark (which as im sure everyone has noticed, is a simple copy of the Rank Missions from XI), we will then get the option to start again with a new nation. I for one LOVED the fact that you couldn't get everything from each nation just by flitting about like a caffeine injected chipmunk, and instead, if you wanted everything, you had to damn well work for it. Nation starter rings were great, loved the Signet system, the little signet staves you could get were a nice touch allowing you to give Signet to your allies, and champion your home towns cause by displaying their banner on your back, and the various pieces of equipment that gave you boosts if you were in a zone that was currently controlled by your city.
All of these things encouraged people to work for their home town, it gave a true sense of community, and also offered a nice little avenue into unintentional RP. Countless times on Ventrilo we would have mock arguments about how Windurst would one day divide and conquer, if those Dhalmel necked weirdo's would just relinquish their hold on the Dunes. All this stuff added a very rich depth to the game, and I for one LOVED going out to try to claim a zone that our home town hadn't held onto in years.
To this day, original Seraphians still speak of the week Windurst claimed Ronfaure for great justice, with the help of the biggest JP, NA and EU LS's on the realm. These are memories that come out of adversity, and we shouldn't get too much freedom in these games, as this leads to what happens in WoW, a community that is devoid of the community spirit, and an every man for himself attitude.
I for one like that you cannot flit between factions, and think it can only lead to a more immersive environment for all, but there will always be the achievement horny, call of duty raging, angry little children who want everything yesterday, and in copious amounts, because they played Rift for 10 minutes and now every game should at least be as boring.