This goes without saying but expecting existing EXP options to work for fast tracking people so they can at least get to the expansion content, seems a touch short sighted.
With how minimal the complexity is on the jobs there isn't much of a reason someone should be stuck running around in a chicken flock doing fates or waiting forever in queues. Viper takes about an hour or so to get the hang of and Picto seems about the same, and the only new ability they get along the way to 90 is one skill that probably could have been there in some lesser form from the start.
They need something like how Death Knight got handled in WoW, where it takes you through some story bit and by the time your done you're caught up. Especially since a lot of people coming to play the expansion have already played FFXIV before and may have ground endlessly already on this existing content.