Requiring any implementation who wants to read the data to be able to run webassembly means the format is ill-suited to any environment which aims to reduce dependencies or bloat.
Is the runtime really that large? I know with wasm 2.0 with garbage collection and exceptions is a bit of a beast but wasm 1.0? What's needed (I'm speaking from a place of ignorance here, I haven't implemented a WASM runtime)? Some contiguous memory, a stack machine, IEEE float math and some utf-8 operations. I think you can add some reasonable limitations like only a single module and a handful of available imports relevant to the domain.
I know that feature creep would almost inevitably follow, but if someone cares about minimizing complexity it seems possible.