You're confusing layers here. fork() is a single line of code in C, but hundreds or thousands of lines in the kernel.
Likewise here, the shell would be POSIX compatible. So you don't sacrifice simplicity at the usage level. My aim is only to address all the feature and performance problems that are driving people to monolithic applications like systemd.
And to do that, new code has to be written somewhere. I believe that there could be less overall complexity in the long run by sticking to shell scripting, rather than moving to all of these unique, complex applications.