It would be very interesting. The question is how they would implement it. Considering 5.0 is the fight with the empire and I doubt that 5.x will be able to cover the entire fight with the empire and eventually bleed over into 6.0.

I would rather Mysidia show up as a full expansion, especially with its lore of mages. I would even be satisfied if they slowly unlocked the region every .5 patch