This is more of an inquiry/concern that I'd like to hear from the FFXIV team answer.
In FF XI there were over 20 jobs to play, and while the variety was amazing, it wasn't a great appeal for many end game content. In past experiences, of all the 20+ jobs, only 5~8 jobs were accepted to hard core/end game raids. These jobs were the most proficient and any other job was highly frowned upon or not accepted.
In FFXIV there isn't an abundance of jobs just yet, but I am cautious as to how adding more jobs will affect the old. I am curious to see how the devs will balance out all jobs, so that end game/hardcore groups will refuse to take X and Y job, because A and B job's kit are much more proficient in that role. This can range from the numbers a job can put out, to the cross class abilities as well as its over all kit. If certain jobs fall out of favor, many players may reluctantly have to reroll just to stay relevant in the current meta.