I recently got pointedrollup, which produces clean builds by assuming the source is using ES6 import/export. It then can mash all the modules into the same closure, instead of the currentbrowser-pack approach that tends to produce a lot of extra boilerplate and closures. It can also tree-shake unused functions.

It would be worth exploring whether something similar is possible in browserify (or, as a plugin/transform independently of browserify).

Big things to figure out:

• a means of resolving to ES6 source for packages written in ES6 and pre-published to ES5. Right now rollup usesesnext:main which isn't exactly standard, and maybe could be named better (i.e. what happens with ES7?). It would also be good to have other bundlers like jspm and webpack agree on the same approach.
• how to take the rollup approach (single closure) rather thanbundle-pack approach (closure per module) and what kind of problems this might impose