Disney has at times promised big things to come that never came to be. Micechat has hinted at big plans coming to WDW, but these haven't been revealed yet.
I've read that big plans are not revealed because then tourists defer visits, so it's better to just build things quickly, though Universal Orlando seems to be the only resort in America that celebrates speedy construction.
So what's the billion-dollar addition to WDW besides MagicBands?
I'd like the whole resort spruced up, including attractions, and the ultimate bike path/rental system built, and billion-dollar, DCA-scale additions for the AK & Studios.