Being able to add arbitrary logic to an otherwise static binary has a lot of interesting use cases. For example Envoy Proxy supports hot-loading arbitrary HTTP filters compiled to WASM into its filter-chain. This allows users to extend the feature set of Envoy, by adding custom logic to request parsing, reporting custom metrics, calling out to other services before forwarding the request, etc etc.
This allows their unique custom use-case-specific code to be managed separately to Envoy, so it can be ported across upgrades etc. It also means that if there's a very particular feature you want that's unique to your business, and wouldn't make sense to contribute to the upstream OSS project, you can write a WASM module for it.
It's somewhat niche, because anything built in this way which is generally useful to many users, will probably just be made a native feature of the host platform. Conversely, anything that does something significantly complex and custom should probably live as it's own stand-alone microservice somewhere. There's still a lot of room for value between the two extremes though!
This allows their unique custom use-case-specific code to be managed separately to Envoy, so it can be ported across upgrades etc. It also means that if there's a very particular feature you want that's unique to your business, and wouldn't make sense to contribute to the upstream OSS project, you can write a WASM module for it.
It's somewhat niche, because anything built in this way which is generally useful to many users, will probably just be made a native feature of the host platform. Conversely, anything that does something significantly complex and custom should probably live as it's own stand-alone microservice somewhere. There's still a lot of room for value between the two extremes though!