This is nice for linear pipes. But occasionally I find myself building more of a graph.

Bash lets you provide file arguments from pipes via the <() syntax (it's turned into a fd reference via proc behind the scenes). And you can also wire up additional pipes with fd renumbering, though this gets ugly in bash, some other shells are more flexible there, e.g dgsh.

A tool to iteratively build a graph of commands and pipes would be the next step.