I suspect some might be able to rise up by injecting themselves at framework level, since it's very likely that the programs will still keep some sort of in-mem

I suspect some might be able to rise up by injecting themselves at framework level, since it's very likely that the programs will still keep some sort of in-memory representation. Though I don't think that injecting code into other WebAssembly blobs is possible with the security models we have today. The surefire way would be an external application that uses OS APIs to fiddle with memory directly (bye bye mobile content blockers). But whatever form it takes, it would have to be programmed to operate on every framework available, so it's way less universal than writing a CSS selector or URL regex.