Heavy Javascript on the client side either means your writing a full featured web app or the entire website is clientside in javascript. The former probably has performance penalties that make this a bad idea. The later, IMHO, is just bad.
The only useful thing I can think of with this is the fact that it can serve up a custom load of libraries all bundled and gziped in one file. But to that extent I can run a small script on my computer that will do that and then upload it to my server rather than having to cross domain half of my Javascript.
Pricing is going to be tricky. You have to convince your users that your service is really worth it. Copying and pasting code into their site costs nothing and takes very little time. Once it's there it rarely changes. Most users don't understand the performance impact of 3rd party scripts.
Why would I use a package manager as a service when I can essentially do it for nothing?
Maybe I'm just not understanding your service. A few years ago, this might have been something I might be interested in (though I doubt I'd pay for it), I think you may have missed the market opportunity.
I really like your description of it as a package manager. In those terms I'm starting to think more like an app store for your web site.
My thinking was more around a company setting where you've got change control processes in place and deployments perhaps aren't as easy to orchestrate/are too much effort.
Then there's my personal itch which is that for every product I build I seem to be doing the same things over and over again with Olark, Woopra, Google Analytics etc.
E.g. I have uservoice, optimizely, ganalytics, kissinsights and totango snippets in my app right now - what UberJS would do for me? Would my biz. partner be able to add new snippets/delete old ones on his own (without interrupting my flow ;)?
Love the idea of getting your biz guy to update things for you. Yes, it would definitely work for that scenario.
Perhaps you should make me love your product, before trying to get me to give you my hard earned money.