I think if AK gets anything else, it should be either a South America section or some sort of Antarctica exhibit. Or an update for the Dinosaur area. But I also think AK is fine as it is for now. You can get everything done there without rushing, but it can still be a full day. A new area wouldn't hurt, but neither would leaving it as-is for a little while. I don't think Zootopia is the right tone for that park, though. For me, the beauty of the park is in the nature aspects and the calmness of it - Zootopia is a really fun movie, but calm and natural are not traits that could be used to describe it.
I think Epcot has enough already-announced things coming that it will be pretty good once it's all settled (although they need to rename the Future World area to something more along the lines of Discovery World). HS could still use one more themed area to round it out (and please goodness do something to improve the flow of the park all the way around), but it just got two new areas and SWGE will keep the park plenty busy for a long time, so HS will probably go down on the priority list for new updates, too.
If there is an announcement of a new big project, though, my hope would be an overhaul of Tomorrowland in MK - once all the other current construction plans are completed around WDW, that's the one area that stands out as being really subpar. It simply doesn't meet its theme anymore. Tron will be great, and Space Mountain is one of my favorites, but beyond that - Monster's Inc. is a cute show, but it isn't about the future at all; Autopia isn't remotely futuristic; Buzz Lightyear is showing its age badly (the guns barely ever work for me and the whole thing pales in comparison to the quality of TSMM at HS); and Carousel of Progress HAS to change that final scene (probably best to just take it back to the original version or something - still won't be futuristic, but at least it won't be an embarrassingly outdated version of the "future" now that we already actually have high-quality VR video games and voice-activated lights and stoves that function better than the ones in that scene). And MK has enough capacity and other attractions that as long as they keep access to Tron and Space Mountain open, they can easily absorb closing the rest of Tomorrowland for a while.