I can tell you about a WebAssembly killer app for a small niche. lichess uses WebAssembly to run a state-of-the-art chess engine inside your browser to help you analyze games [1]. Anyone who wants to know what a super-human chess player thinks of their game can fire it up on their desktop, laptop, or even phone (not highly recommended, it's rough on your battery life).
Obviously very serious chess players will still want to install a database and engine(s) on their own computer, but for casual players who just occasionally want to check what they should have done on move eleven to avoid losing their knight it's a game changer.
Obviously very serious chess players will still want to install a database and engine(s) on their own computer, but for casual players who just occasionally want to check what they should have done on move eleven to avoid losing their knight it's a game changer.
[1] https://lichess.org/analysis