Of course there could be some tweaks like a scoped eval to prevent stomping on the script's variables, but it's really not very hard for a C program to escape s

Of course there could be some tweaks like a scoped eval to prevent stomping on the script's variables, but it's really not very hard for a C program to escape shell variables correctly and safely. You could have an eval that only read variables, but trusting a program to only return variables is a really low bar; it's very hard to mess that up.