Nothing has been explicitly stated yet on what the prerequisities of Module 4: Tyranny of Dragons will be in order to start the campaign progression.
Campaigns one and two, Sharandar and Dread Ring, had no pre-reqs – you simply grabbed a quest from Sergeant Knox to lead you to the new zone. Module 3: Icewind Dale changed this. It positioned the Icewind Dale campaign above the other two – you have to complete three boon tasks in either of the earlier campaigns before you are deemed ready to venture to the frozen North. You also have to have a gearscore of 10000; not that hard a task if you’ve done any epic level dungeons but a potentially expensive auction house shopping trip otherwise.
So my big question is whether Module 4 will turn this into a trend for future content. Will the gearscore requirement be even higher than 10k? Will we have to have completed any boons from Icewind Dale first? In both cases I hope not. I deem Neverwinter to be a very casual-friendly MMO, I think the devs will have misjudged their largest audience segment if they start imposing very onerous requirements on entry to new content. This is story content as well as a source of new gear after all!
I doubt they’ll have Module 4 completely unlocked with no prereq at all, it’s more likely it’ll be at the same level as Icewind Dale for difficulty and prerequisities so that those who dislike IWD or have spent far too much time grinding the content for rare drops can bring their new warlock alts through the new campaign without having to progress in two campaigns as a barrier to entry. I am looking forward to finding this out soon.