I lasted a matter of weeks in FFXI before giving up on forced grouping in the notorious "Dunes", so I'm not entirely qualified to comment on the state of the game. Fortunately, Massively points to a survey of people who CAN comment on the game, Square's official player survey.
There's a fair chunk of interesting data in there, but one pair of stats jump out.
- According to the actual server logs, over 85% of characters log in for no more than three hours per day, with an average for all characters of 126 minutes. That's obviously not an entirely trivial number, and it would be interesting to see how that 85% breaks down (e.g. if a large number of those characters are actually only on for a couple hours per week, with the rest sitting just shy of the 3 hour/day mark). Also, the number might be artificially deflated by the use of mule characters, since storage in FFXI can be a nontrivial task. (Note that, unless this has changed recently, there is a monthly fee per additional character; mules seem to be at least somewhat popular regardless.)
- Meanwhile, over 25% of players cite solo ability as the reason why they chose their "job" (class in other MMO's). This made soloing the 2nd most popular choice in the survey, trailing only the generic "it's fun". There may be some selection bias in this sample (i.e. perhaps solo players were more inclined to answer the survey in order to advocate for more content/dev support), but it's still striking to see such a large response in favor of soloing in a game with a strong reputation for mandatory grouping.
Suddenly, the decision to emphasize solo play in the forthcoming FF XIV becomes crystal clear (pardon the FF lore pun).