I wish I could do that, but there are a lot of emulators that don't have web versions, and the launcher and related scripts are very heavily dependent on a Unix-like OS and there is no way to port them to JS (a completely separate launcher and scripts would have to be written).

It sucks that there's no good way to port Linux directly to WASM UML-style, since WASM insists on implementing memory safety at the bytecode level with no way to bypass it. There is a very limited port, but it doesn't support paging. Not all the emulators would run on a full-featured WASM port if one existed, but that could be dealt with by just using user-mode QEMU to run whichever ones are x86-only.