If Avatarland cost around $.5 billion (that's what I seem to read fairly consistently), it may not take as much money as some of us fear to bring EPCOT up to snuff. That land is beyond immersive and is really staggering to behold in many respects. Most area's of EPCOT wouldn't require that level of theming to finish them off. France ride, 2 other country rides/attractions, put at least a movie into the countries that don't have any attraction (I think that's 3), overhaul UofE (this may approach $100 million, but shouldn't), Imagination overhaul, bring back WoL and clean it up of course, overhaul Innoventions, improve Land and Living Seas seem to be the necessary improvements (at a minimum) to bring this to a full day park for all age groups. That's 12 additions, and even at $100 million each (it shouldn't come anywhere near that), you're only looking at $1.2 billion. I don't mean to make that sound like nothing, but compared to what's being invested in other parks, it isn't that far out of line at all.
Beyond this, one of the questions to look at, is are we trying to encourage people to visit all of the Disney Parks as separate vacations, or can we put the same attractions in multiple parks to save design costs and time? I enjoy a good
Disneyland venture, but I'm not going overseas to go to Disney. Those rides could be duplicated here and vice-versa and have no impact on my enjoyment. That might save some cost for the company be reusing some designs in multiple places. Just don't make DL and WDW the same please.