[sltkr]

Great point!

Actually this observation invalidates the whole setup. Because even though you could define /bin/sh itself as:

    #!/bin/busybox sh
    exec /bin/busybox sh

Then you still cannot use #!/bin/sh in any other shell scripts, because for historical reasons the interpreter of a script is not allowed to be another interpreted script, it must be a binary. So /bin/sh pretty much has to be an actual binary.