I would try to use JavaScript tooling in JavaScript projects, especially if I share it with other developers.
I would love to see better handling of filename transformation, file watching, and parallelization.
A few times over the years I had given up and just used Make instead of Gulp or Grunt. Most recently, I wanted to watch if files had been deleted (if directory entries had been modified). It ended up being a few lines of Makefile.
And once you understand the syntax, it is expressive and simple, and way more portable. There was some good discussion awhile ago on this[1]: