If memory serves,
DCL tried that at one point and it was massively unpopular and so they went back to it being included. I doubt they would take away soda (its so cheap) or juice and tea.
I do think a drink package might be coming and that I could see DCL making serious money on it. Many people like things that feel all inclusive which is why so many people pay for the dining plan even if is often not a good value. I do not think the majority of adults would get sloppy drunk but a few might; however I have seen that without a drink package- heck I was tipsy at a trivia once coming back from Cozumel (I thought the margaritas were more watered down than they were and they did not hit me until later


). A drink package could be a money maker for DCL- I think ppl will assume they will get more drinks than they actually will have time for.
I have been pitching a once a year adult only sailing for awhile (and yes there are ways to do it with the spaces not being an issue). I would LOVE for DCL to offer this (off season, on whatever ship they are struggling to fill, and even at a higher than normal DCL mark up it will sell out ASAP). DCL would need to market this as a special sailing with unique offerings similar to a DVC member cruise but I think it would sell as fast as the panama sailings do (if not faster)