What's the alternative? To use absolute paths for everything? That seems kind of tedious, and may be slightly less performant if the kernel has to do more dentry lookups.

I think the idea of a current working directory is a reasonable one, it's just that the limitation that a process can only have one CWD at a time is kind of arbitrary when you think about it.

I could even see having commands that take multiple CWDs. Like a move operation could take a source and a destination CWD as an alternative to specifying source and destination paths.

Directory file descriptors already exist. I wouldn't call them "current working" directories though. Are you suggesting an expansion of those, or something different from those?