They encountered a ton of issues that delayed the start of Pandora years ago. As this is Disney, again, expect 95% of the land (s) to be completed before they open them.
Whether too long or too short, Disney will go at their pace for construction. None of us want to vacation and look at scrims the entire time. That said, IMO, I believe they have too many projects going on at once. They needed to care for the existing rides first, then introduce one expansion, then another. Unfortunately for all of us, they threw everything on the board at the same time.
If they did one thing at a time, they could more than likely do a quality job in a shorter time frame, but they didn't do that.
So that means we're stuck with DHS as a construction zone, Epcot FW is sorta empty, Frozen-way will open this summer in the WS, AK can't get Rivers of Light up and running and Pandora is a Pandoras box. This leaves the MK for everyone to be stuffed into. Yes, they shouldn't have cut staffing, but there just comes a point where there are too many people and not enough things to keep everyone entertained/happy. This is why FP+ can be seen as a failure due to the lack of options in other parks. Things will get better, but the key is patience. If you can vacation knowing you might not get to everything and you are able to wing it, you'll be fine. If not, then I wouldn't suggest visiting until about 2019 or so until these simultaneous huge expansions are nearing completion, and that's if things go smoothly between now and then.