You're apt to be disappointed on that last point then; leveling is being pushed even further toward quest-based leveling from what they have said, which is more likely going to continue to be a solitary affair. That said, in version 1.x, of the three jobs I managed to get to 50, I leveled in parties on two of them from 35+ and the other from 40+. Leveling in parties is loads faster already, although hardly necessary. It becomes even more unlikely when you consider that the party-dependent leveling is extremely unpopular in the current MMORPG landscape, and most players probably won't put up with it being required.