Nope. Despite the 28 'likes' and all the numbers, I will strongly disagree with you on this -- at present.
WDW has one park, with considerable room for expansion, that is generally overcrowded. And it has three others that not only are not, but have vast areas that either haven't been developed (DAK) or have been allowed to sit empty (the others). I'd argue, and quite well, that until WDW balances its crowds and gives people compelling reasons to visit the other parks, there is nothing to suggest a fifth gate is a remotely viable or practical from a business POV.
Americans, who still make up the vast majority of WDW visitors, don't have unlimited vacation time. Additional parks will cannibalize current visitors and, yes, future ones. There isn't a financial reason for adding a new gate any more than there is a compelling creative one (considering that only DAK comes close to being a cohesive themed environment today).
After you have four healthy gates, then we can talk about whether it makes any sense for an additional gate. My strong opinion is that even a decade from now, all we'll be doing is talking. The idea that WDW needs five parks to deal with ever increasing masses of humanity is far more simplistic than your usual spot-on analysis (don't take that as an insult as it reads harsher than intended!)
WDW needs, desperately, new and compelling attractions and entertainment across the four parks it has (yes, even MK needs more ... a lot more!) It may even need a third water park, although I'm not convinced of that either. It needs infrastructure (everything from road work that is finally happening to a transport system not based upon buses).
It NEEDS those things to be healthy and thrive.
It doesn't need a fifth gate, no matter how you torture those numbers!