If I recall from maps, there really isn't anything "in" the train loop besides maybe a road? If they got rid of the train, seems like a lot of space for an expansion? AK needs it I think despite Pandora.
I am of two minds on this, for that matter on DHS as well.
First, lets be clear, I agree with almost all here, that DHS, then Epcot then AK needed more. That is my order by the by, maybe not most here
Second - I am fearful of just adding more to parks after a major add. AK just got Pandora, and it is beautiful. Part of me wants to let the park breathe, then add more. I would personally love to see an austrailian or New Zealand add to the park, with maybe some kind of coral reef water ride(just my guessing...).
third - same with DHS. Do NOT get me wrong, once SW:GE opens, DHS will be a bloated fish waiting to sweat you. Crowds will be enormous. The adds of TSL and MMRR will help, but it will still be a mess. Adding even more construction will IMO only make it worse. I would much rather the park breathe, and then expand some more...updated Indy ride to replace stunt show, and some ride or add in the animation area.
Last but certainly not least(well it is for me as I am NOT and Epcot fan

) - Epcot for sure is adding: FW -added theater to Soarin, GotG, Space restaurant, updated Mission space - rumored to also include - update to SSE, update land, potentially an add to WoL, and spine redo. Meanwhile WS - confirmed - new night show, Rat in France, Gondola, and not too long ago Frozen redo. Rumored adds - Brazil(with ride, possibly India(possible Jungle book boat ride??), UK ride OR Coco overlay in Mexico.
so that is a whole lot for parks that have basically been ignored.