You can write a replacement for gulp in Perl 6, but if it doesn't have the plugins, who will use it?
Grunt and gulp have huge plugin ecosystems, which is both a blessing (you can find ready-made plugins for a lot of tasks) and a curse (everything moves very rapidly, plugins get abandoned, blacklisted and superseded all the time - if you want to compile TypeScript files, half the blogposts will recommend gulp-tsc .. but wait, it's been blacklisted, you should use gulp-typescript instead ).
Grunt: ~5400 plugins: http://gruntjs.com/plugins
Gulp: ~2000 plugins: http://gulpjs.com/plugins/
Gulp's list of blacklisted plugins: https://github.com/gulpjs/plugins/blob/master/src/blackList....