Parallel and sequential, especially at the command level, are really the wrong abstractions for running scripts. If you have multiple packages, each with builds, there's a high chance you have dependencies and multiple packages depending on common ones.
What you really want is a way for scripts to describe their dependencies, and then the runner figures out what order to run them in, and cache scripts that don't need to be run because their inputs didn't change.
Wireit[1] is an npm script runner that adds that incrementally on top of package.json. I can't manage an npm monorepo without it now.
Deno started integrating the idea directly into their built-in script runner. I think this is an important enough feature that more runtimes should follow Deno's lead.