What risks do you see?

BTW, the idea is not radically new. Java loads classes only when they are accessed first time.

Operating systems load native applications by mapping executable file into virtual memory. The pages are loaded into physical memory only when CPU tries to access them.

Ok yes, if there's a mechanism that dynamically loads the missing parts then it could work (actually emscripten supports dynamically loading scripts similar to DLLs). But 'naively' deleting functions from an asm.js blob would result in some 'unknown function' exception if the analysis was wrong and a removed function is still called somewhere.