I have been on th been on the Destiny 3 times and know of no one being able to upgrade to all inclusive. The best thing to do is get it included in the price of your holiday. I never pay for mine and it is the best thing to have on hols we are not big drinkers but i like to be able to leave a drink if i dont like it. Have a great time if you go, we are off in jan to the caribbean with the destiny.
I would seriously think about upgrading to ANOTHER SHIP before you book! Of all the ships in all the world, you have to cruise on this one? Have you read the number of negative reviews about this ship? Happy cruising.