I don't think he will ever be Duke of Sussex either. He won't be royal, I think the LPS would have to be there to cover the fact that in a tragic accident that wiped out his cousins he could be next on the list and be upgraded. I like the fact he isn't titled, I think it's in keeping with a modern Britain. And makes a mockery of all those insane aristocratic titles still hanging around. Time they went or people stopped using themy except for work.
Of couse he will be Duke of Sussex if he outlives his father... unlss the monarchy comes to an end and theres a republican govt which bans the use of titles.