I'm sure real-time rendering will be useful in a variety of use cases. However, one of the main reasons I use LaTeX (when I did) was because it allowed me to separate creation of the content from worrying about the format. This meant I could switch between author and designer without my (feeble) focus being distracted by an image jumping around or an equation overflowing. Indeed I actually found 'compiling' a LaTeX document quite exciting as I anticipated how it might look.