You mean it's not on rails now? Currently people grind/leve combat jobs to 35ish, then do Raptor parties > Natalan Spirit bond parties. There isn't a lot of pathfinding and exploration going on anyway... once people find a workable solution to a problem (ie finding the fastest way to level), every bloody person follows the template. So yes, I'm going to go out on a limb here and say that FFXIV players are just like the majority of most MMO players in that you don't really give a damn about the lower levels, and your biggest goal is to rush to end game.

Now if you're looking to take it slow, you can definitely still grind on mobs. It just won't be at the fastest speed possible. The days of standing in a corner in Valkrum and killing crabs for 200 exp a pop are over. If you want that group feeling, we'll actually have lowbie dungeons where you'll have to do MORE than just stand in the same grid square killing everything that spawns. Right now, we really only have Toto-Rak, which largely goes unused for leveling (instead it's a 2 man seal farming location)

In addition, I know people who have several lv50 classes/jobs and they still have yet to complete their main/GC storylines. Why not give players their storyline (in brief chunks) along the way to 50? One other note, I truly doubt they'll add enough quests to take every combat job up to 50 by questing alone. So that's where you fill the gap with dungeons, leves, and yes, mob grinding exp (although that will be the least attractive option).

I know some people have this amazing aversion to anything WoW does, but it does get silly. I wonder if some people have the idea that ffxiv is a sandbox MMO (which it definitely isn't, but will be getting sand box elements come player housing etc). It's a theme park, no matter how you dice it. That's not saying it's bad to have a theme park MMO, especially if it's well done.