If I link a program dynamically to a LGPL library (here GTK+/GLib), I'm allowed to distribute the program on my own terms (non-copyleft).
Now, the LGPL library provides loadable modules. Place a shared library (.so, .dll, .dylib) in a certain directory, and it will attempt to load it, using a well-defined interface. Am I allowed to distribute the plugin module (dynamically loaded by the LGPL library) as closed-source, according to the terms of LGPL?
I'd take care that I don't use code from the LGPLed library in my plugin, and only include such headers that would be permitted by the license, and which I could as well use in a closed-source program ("3. Object Code Incorporating Material from Library Header Files.").
I am well aware that you shouldn't take legal advice from strangers on the internet. I am asking this mainly because I'm curious. No code has been written, and no business commitments have been made at this point. Before I do anything real I probably should ask a lawyer (but they're quite expensive for just satisfying your curiosity!). I do have confidence though that I can get a good answer - maybe someone has done exactly this thing and can report on their experience. Maybe there is a definite answer from the horse's mouth (FSF) that I overlooked. I'm writing this disclaimer so that you don't have to, so please don't tell me to ask my legal department (which I don't have as an individual).
And if this rather belongs on Programmers.SE, please feel free to move. I posted this here because there might be some technical (linking) issues that are important.