If they think there's a market that will pay £1,799 for it could quite easily happen next year. I don't think there's any technological reason it can't (space on the logic board for requisite number of chips?). Ultimately it depends on if the number of people that will buy it at the price they charge meaningfully exceeds what it will cost to design and produce. Assuming the sums don't add up currently, I would still expect to see a general move up to 128/512/1TB at some point (upon the introduction of 8K video?).
As a related aside, I wonder if they will go straight from 512 to 1,024GB or if there will be a 768GB model as the top storage capacity for a while?