Takamasa,
I don't work for 10gen, so I wojn't comment on license or legal issues. However, I will add the following comments.
I would personally find a COM based mongodb driver for VBA potentially useful in excel documents. I don't think I'd ever use it if there was not a free version. Being able to interact with mongo from VBA is useful to me.
As far as javascript from windows scripting host, this could really be useful in conjuction with linqjs. I happen to do all my windows scripting in powershell, these days.
If your going to market this for windows scripting host, you might want to base the object model on the nodejs API as you further evolve this driver.
Justin