Wow - so much speculation!
Don't get me wrong, I feel for everyone. But, it should be remembered that any cruise line has the right to cancel or change an itinerary at any time. It's funny because that's part of the irony with people like us. We are so organized and book so far in advance because we're planners and we want the security of knowing what will happen. On the other hand, we don't often consider the risk of booking something so far out and how it could change. It is truly frustrating to have plans change, but that is the risk we take in booking so far out.
The positives are to remember that:
(a) it is too far out for airfare, so it's guaranteed that no one has airfare yet that will be affected
(b) a cruise line can change an itinerary at any time WITHOUT compensating passengers in the least. Heck, you can be on your sailing with shore excursions booked when the captain changes the itinerary. Yes, you get your excursion money back, but you get no compensation for your itineerary changing and not sailing where you paid to sail to. The fact that Disney is giving shipboard credits is GREAT! As a
travel agent years ago I knew people who had plumbing problems in their cabins and stuff on different cruise lines and got diddly-squat in compensation!
(c) although things like planning to sail for the holidays are definitely affected, it's not as though they're canceling the sailings for this month where people would have to fight with their jobs to get new vacation times, etc. That they're doing this a year out is actually a good thing. Granted they could give you a little more time to make your changes, but at least they're giving you time
My curiosity lies more with people who booked using their DVC points. Once you book a cruise with DVC points you can't get them back. So - if these people can't change their dates, is Disney going to make an exception and allow them to get their points back or are they out of luck and lose their points? It would be REALLY wrong to not turn the points back into reservation points.
Did anyone book any of these sailings with points and know what's going on with that situation? (Just curious)
As for Alaska - of course they can have the ship in 1 port most of the year and then move it to Alaska for the summer. ALL cruise lines operate this way for Alaska. Alaska is seasonal and that's just the nature of that particular itinerary. All cruise line's reposition their ships for the season and then move them back, so there's no reason Disney couldn't or wouldn't do the same.
As for moving out of Mexico - I personally don't think that can or will happen, at least not for a couple of years. First of all, they have a contract with San Pedro and can't just leave. Second, the amount of marketing and advertising to promote the new Mexico sailings, plus its merchandise, etc. far exceeds anything they might be losing in sending ships that aren't 100% full. Remember, it's not even been a year since they started this itinerary. I would agree that their extensive use of the KSF promo on this itinerary does show they've had a little trouble filling it, but once they release the promo the sailings have been selling out super quickly. It is more likely that there is an itinerary gap that needs to be filled for this time frame and the Wonder is the ship to do it. It happens all the time in the cruise industry (a unique itinerary opportunity comes up, they get an opportunity to test a new market, another ship gets scheduled for dry dock and a different ship has to pick up some slack...there are hundreds of reasons). At this point EVERYTHING is speculation, and we won't know until they announce it.
Anyhow - that's my 2-cents. I truly am sorry for those of you who had plans and don't know what to do with your vacations now, but I have faith it will all work out for you.

Just take it in stride and try to make the best of it. I am definitely curious to see what's going on - it will be interesting!