What I think they should do is, from the start, allow people to 'trade' servers with each other after being allocated one. That way the populations will be stable but friends can hang out with each other without much trouble. Some servers might end up 'in demand' on some level but hopefully over time it wouldn't be so much of a struggle, and they could at a cheap cost allow for people to transfer without a 'trade'.

No idea if it would be workable, though.

I imagine in FFXIV there will be some easy way to play with friends, though, otherwise it would be a bit stupid overall as all the FFXI LinkShells would get screwed over.