... are there any use cases for using pure Python bytecode inline?
Yes. Sometimes you can handroll a little faster code than Python normally generates on its own.
Also, you can gain access to the loop induction variables for list comprehensions.
Here are some links to get you started: https://www.google.com/search?q=python+bytecode+hacks
If you would like to make the bytecode manipulations programmatically, here is an optimization recipe that shows how to go about it: Decorator for BindingConstants at compile time
That said, if you care about speed, the simplest speed-up is often to run pypy instead of cpython if your application allows it.