Do you know what I do?
I use zsh. Let's say I need bash. "bash<Enter>". I'm in bash :-) I need cmd (yup, that can happen). "cmd<Enter>".
I need to run just one command with bash: "bash command<Enter>".
I need to run just one command with cmd: "cmd /c command<Enter>".
These problems are trivially solvable :-)
I'd like a way to get all the benefits without the cost or any extra required effort for the user.
Some painless master shell program. No epiphanies yet though.