DCL is soon to welcome 3 new boats. They are looking for a new island because of this. I suspect they are also interested in developing it in a similar way that
Royal Caribbean is revamping Coco Cay, water slides and premium restaurants and such. They can't do that on
Castaway Cay due to the lease agreements.
I agree with above that right now opening a property outside of WDW or another Disney location is just not in the cards unless they stop filling them so readily. Also the article specifically states that it is DCL employees doing the scouting for a new island. They are different companies, they don't all work together (which reminds me of a moment where someone on our last cruise assumed the entertainment director also worked at WDW since she talked about going there).