We already have an Everything App that allows you to execute all the different functions of your phone, it's called the operating system. The proposed app would just be a smaller, shittier OS with fewer functions and no choices. Elon is a failed Steve Jobs—which is depressing because Jobs was also a charlatan—who thinks "what if it was one thing" is actually the answer the all technology, because he doesn't understand technology as well as he thinks. Pro tip: carrying around 1 device instead of a cell phone, a pager, an mp3 player, and a PDA is helpful. Consolidating different functions that have no reason to interplay with each other into a big mess is not.
tl;dr it's shit from a butt