"GPL makes it impossible to utilize the library in any way in a commercial product"
That's not strictly true. You could license your commercial product as GPL, or (more likely) contact the library's authors and negotiate usage of the code under another license.
I'ts not just "not strictly true," it's not true at all. Nothing in the GPL prohibits GPL'd code from being used in commercial products. What is prohibited is using it in proprietary, closed-source products. You can have a product which is both F/OSS and commercial. Ask Red Hat, for example.
You are right, of course. "commercial" was the wrong terminology; I meant proprietary, closed-source products as you said.
However, whatever your views on closed source products, they are still quite prevalent. IMO LGPL is a great license to get support from companies that sell these products, while ensuring that your software fundamentally remains free.
With JavaScript and the GPL it is very unclear what "linking" is. Probably your entire website becomes GPL including content. Who knows as the language was written for system libraries. So I can see lawyers having an issue.
If you are not intending to modify Mongo then AGPL is not restrictive, which may be OK. The database API is not usually considered as "linking" as it is a wire protocol.
As the OP has demonstrated, "Contact the library's authors and negotiate usage of the code under another license" is EXTREMELY difficult for a project maintainer and would thus be near impossible for anyone else.
It is much better if the price and terms are simply public up front. For instance, we were worrying about PyQt (GPL + commercial option) vs. PySide (LGPL) for a project, where PySide didn't support certain things that we needed. But then we realized that the PyQt commercial license comes with reasonable terms, and costs only £350, and it wasn't even worth the time worrying over it any more.
So yeah, "contact the authors" can be hard, but an up-front agreement and price can make it pretty easy.
This is how the x264 developers do it IIRC, they offer x264 under GPL and if you want to use it in a proprietary manner you need to buy a licence from them in order to do so.
That's not strictly true. You could license your commercial product as GPL, or (more likely) contact the library's authors and negotiate usage of the code under another license.