Rollup Esri

//Gulpfile.js

const gulp = require("gulp");
const rollup = require("rollup");
const sourcemaps = require('gulp-sourcemaps');

const nodeResolve = require('rollup-plugin-node-resolve');
const commonjs = require("rollup-plugin-commonjs");
const babel = require('rollup-plugin-babel');
const replace = require('rollup-plugin-replace');

gulp.task("scripts", function () {
	return rollup.rollup({
		entry: "./src/js/main.js",
		plugins: [
			replace({
				"process.env.NODE_ENV": '"development"'
			}),
			nodeResolve({
				main: true,
				skip: [ "esri" ] // Let Dojo handle Esri
			}),
			commonjs({
				// non-CommonJS modules will be ignored, but you can also
				// specifically include/exclude files
				include: "node_modules/**"
			}),
			babel({
				exclude: "node_modules/**"
			})
		]
	}).then(function(bundle) {
		bundle.write({
			format: "amd", // AMD is Dojo compatible
			dest: "build/js/main.js",
			sourceMap: true
		});
	})
});

Also made mods to index.html to support rollup

    <script>
        var base = location.href.replace(/\/[^/]+$/, "").slice(0, -1);
        var dojoConfig = {
            parseOnLoad: false,
            async: true,
            cacheBust: "0.0.1",
            packages: [
                { name: "js", location: base + "/js" }
            ],
            deps: ["dojo/domReady!"],
            callback: function () {
                require(["js/main"]);
            }
        };
    </script>

    <!-- ArcGIS api -->
    <script src="https://js.arcgis.com/4.0beta3/" async></script>