Hm. I can kinda see it replacing self-extracting EXEs, but a lot of why you choose specific file formats is for specific features they offer - any self-describing system can fall into "there are too many competing features and nobody handles them all" exactly as easily as any other format.

Like, can this file be efficiently mmap'd? Maybe if it emulates tar internally, but you don't know until you run it. Can it be seeked to specific bytes to only decompress part? It only supports a pre-release version of ISO-36898533 seeking, and your file library dropped support for it 6 years ago. If I rewrite 1MB in the middle, can it only change those pages on disk (and maybe an index), or do I have to rewrite the whole thing? Well the wasm blob supports 97 different APIs for it (there are 35 copies of one with different names), so it's larger than the data (but nobody paid attention to that), so you have 19 options that you recognize, but your CPU's native WASM accelerator only handles two or three so you've still got to specialize your code heavily.

At least with "*.tar.gz" you have some idea of what's possible.