One thing that always bugged me about XI is that with all it's jobs out, there only seems to be room for like a third of them now if you want a slice of endgame. If your favorite job happened to be RDM(post WotG), DNC, NIN, BLU, DRG(post Abyssea), or dare I even say PUP, your fun of the game is going to take a dive unless you can prove yourself and even then, ignorance will prevail or level another job (even if you hate it) just to get the gear you want. I don't want to see that kind of thing happen to ARR, we've already seen a taste of it when BRD and PLD were the go-to jobs for coil and the doom/gloom said jobs expressed when adjustments were coming.

Plus there were activities where you had to wait, and wait, and wait for that right setup... or people to log on to gather. Some players don't have that kind of time, at least not anymore. I feel that XI is only going to be for the ones who have more free time than most and it will turn into a very niche group like the way Everquest end up, or so the legend was told. They have made XI more casual friendly, at least more attractive to newcomers and old players who quit around Abyssea.

One thing that I did wish ARR took from XI is the open world feel. Dungeons feel like wasted potential because they're instances. XI you can literally get lost inside Castle Zhval or Kuftal Tunnel running into NMs, however ARR is still fresh so this opinion is at best premature.