I just called DCL to book using an OBB placeholder. (When I tried to do it online, it just kept kicking me back to the "retrieve reservation" page; when I mentioned this to the CM, her response implied that this is expected.) I was on hold for about 45 minutes, so call volume is not exactly low. When I eventually got through, the CM told me that it was her first 2017 reservation. She said that bookings were really slow yesterday; they had lots of inquiries about summer 2017, but not much interest in the earlier dates.
As for price:
Fantasy - March 18, 2017 - 7N Western
Cat 5E
2A/2K (8, 11) - $5719.92 ($1858.50/$762.30, taxes $478.32)
includes OBB / no transfers / no insurance
For comparison, we booked a Fantasy 5E Eastern in March 2014 for $5645 (no OBB), and Magic 5C 7-day Dover/Barcelona this past summer for $6676 (w OBB). Both of those were opening day (for general public) prices. That Magic reservation was originally made on board for a March 2015 Caribbean cruise, and I recall the price being around $7000 with OBB, though that would have been well past opening day.
So while today's price is high, it's not drastically out of line with what we've seen over the past few years. For us, the drop in the CAD makes the actual cruise fare difference look almost insignificant.
Personally, I think you're right. These cruises will sell, eventually, but probably not to people who have done it 11 times already. At the same time, I'd take the slower booking rates and my own price history as indications that Disney's ability to continue to raise rates is limited, at least for status quo / non-holiday itineraries.