My guess is that they won't make skill trees for Jin or Sieghart. Neither of them have 4th jobs, so it should really come after. If a skill tree were to come next, Amy ftw?
I also think that a new continent would be a nice, but they have to do more than just planning the first dungeon, they have to think ahead and plan every other dungeon too, on the map.
I hope they give Sieghart a 3rd class. o.o