Please don't charge for module usage. Perhaps a membership fee or donation structure? Do you know what the commercialization will look like?
The future is large, but I can pretty much guarantee that paying for access to open source modules is not ever going to happen. Not because it's evil (though, I believe is), but because it's stupid. It's just not a good model, and it's not hard to see why. No one wants to pay it, and rather than deliver value, you're making people go elsewhere. It is a case of the orchard selling lumber, burning down your value in order to get a short-term gain that can never expand.
Many companies have been literally begging for me to figure out a way to take their money and add some features to npm. None of this impacts what any of you are currently doing, and in fact, it helps you, because it requires building additional high-availability systems that are robust enough for the *next* 10x increase we face.
Like I said, all that is currently free will remain free, and all that is currently flaky will improve. There'll be some new stuff you can pay for if you want to use it, but if you're happy with the current status quo, you can just take it easy and maybe eventually get a job where you use npm for work stuff also :)