In an ideal world, two things would fall into place: the LFP flag system (whatever it is) works as intended and is used by the general populus, and party based exp (dungeons or standard grinding) is worth just slightly more than quests (I'd personally balance it around 1.2:1 dungeon:solo). The convenience factor of questing will make it the prefered method of gaining levels solo while looking for a party, while dungeons and/or grinding (depending on your preferences) would trump solo exp when availible.

Reguardless of how fun or not fun you may find party grinding (dungeons or otherwise). It's an important step that has been lacking in a lot of MMOs. Very little of classical "end-game" is solo oriented. As such, if the entire leveling process is done solo, your training and initiation has to overlap what would otherwise be when you should be doing "end-game". By giving players incentive to party earlier, the game can introduce party mechanics at a more gradual pace.

As to the concern at hand, I believe it was stated that there would be serveral dungeons specifically for the purpose of leveling (and gaining some basic low-level gear presumably). If that is indeed the case, it seems extremely unlikely to me that they have dropped the concept of party exp entirely for quests.