I'm definitely against boosting characters. FFXIV has a fair amount of rotations and gameplay to learn to just jump in at level 60.

However to make things a bit smoother for alts/new people there are a few things they can do.

1) Smooth out the 2.x MSQ. There are a lot of fetch and carry and other quests (repairing f'lammin's earring, fetching the refugees from vesper, tataru's mining) that don't belong as part of the main story and should be changed to be side quests. Still there for anyone who wants them, but skippable for those who just want to move on.

2) Put a smuggler in Coerthas that's willing to smuggle you into Ishgard for a price. Requires a level 30+ battle job. This will let people unlock the new jobs right away, and get to play the story as the job they want, rather than have to level all the way to 50 (52 or 53 now with the xp MSQ gives) on a job they dont care about just to have to turn around and then grind 30-50 again. It will also give crafters/gatherers access to HW mats.

3) For 4.0 make sure that the jobs/most areas are NOT locked behind the story, just the quests/dungeons, so that they don't have a repeat of people being frustrated with leveling. As someone else posted, it would be nice to also have some mid level/all level(stuff like palace of the dead) content come with the expansion as well. For both the new jobs to play in, and for people who aren't cap yet.