The Great Betrayal!

[Alberel]

For Plot reason I think they need something to drive our character into the position where we will be forced into the new Flying Continent or so we can start out in 3.0 without all our Warrior of Light powers we gained from the Echo and political power we gain from the Scions.

The Warriors of Light are basically God/Goddess among people now since they are the only ones that can defeat the Primals and complete "impossible" tasks that no one that do not have the Echo can achieve.

Think of 2.5 part 2 plot most likely as their way of Nerfing the Warriors of Light's Plot Armor just for 3.0 storyline until they gain back that Plot armor later in 3.0 Main Scenario.

We already have a reason to go to the expansion areas though. Ishgard is going to come under direct attack from Dravania and we go to their aid. The flying continent is Dravania itself for the counter-attack. Since all of this would appear to be orchestrated by the Ascians we have a motive for helping.

As for us losing our WoL powers I don't see why we need to. We've had the same powers throughout 2.0, they haven't changed or grown at all. All the echo lets us do is resist tempering by a primal and see the past where it's useful to do so for plot reasons. Without the echo we would lose instantly to any primal and would not have a convenient excuse to get flashbacks. It won't happen. If anything we'll discover what the echo actually is seeing as the Ascians also possess it and have the ability to give it to others...

This isn't a manga-style power creep problem. The WoL has not gotten any more powerful in a story sense so has no need to be 'nerfed' within the story.

With regards to the OP's betrayal thing... I see no reason to think that based on the trailer. The current Scion headquarters is not a secret so for Nabriales to break in and steal Louisoix's staff would not require betrayal. The scene in Ul'Dah is likely the Monetarists finally putting their 'revolution' into motion which is not a betrayal since the Scions and the city state leaders have all known about it for ages, they just didn't know what to do to stop it.