I admit, I don't follow discussion/commentary as close as I could (so this might have been covered somewhere), but it looks like there aren't any guest passes available for the expansion quests.
I'm rather hoping this will change at some point, sooner rather than later. My guild is pretty casual and the half of us who keep active VIP subscriptions (or, in this case, purchased the expansion) frequently buy guest passes for the half who can't/don't... and as it stands, that means that we're not going to be able to do any of the expansion content as a guild for the forseeable future.
In a more general sense, the expansion is a pretty big commitment - 2500 TP even for the basic quest bundle. I'm sure there are a number of people who don't have it yet who would be more likely to make that purchase if they could preview some of the quests first - which is the exact mechanic that guest passes allow in every other adventure pack in the game.
All told, I'd say there's a pretty major case to be made for making passes available, in some form.