I found this thread, and realize it's a little older but I have discovered the same issue with final payment due date on a Viking cruise. I booked in a couple of months ago and just realized the final payment is due in early 2024 but the sailing is later in 2025; making the final payment due a full 18 months in advance. I called them, thinking it was a print error and they meant the same date in 2025, which would be 6 months in advance. But, they confirmed it's 18 months. In addition to the risk of paying that far out as well as the loss I'd experience on interest/growth of my hard saved earnings, I didn't budget for this trip in early 2024. I booked it in the year I planned to pay for it, as my travel budget for 2024 is already spent or earmarked.
I realize I could cancel and then rebook in a year and see when they would request final payment (whether immediately or within 6 months of departure). By then I would be comfortable parting with the funds. But, the price of the trip could go up or it could even sell out. I'm a bit disillusioned based on what I'm reading on this thread. Anyone ever try this tactic - cancel and rebook later? Changing cruise lines isn't really an option at this point because I'm going with friends (though I booked into a solo cabin) and this is their selection,