Comment 9 for bug 728426

It's quite possible to have an extension that is maintained by the core developers. and it's probably just as well to have printing as an extension/plug-in/add-in for two reasons: One is maintainability, and the other is that users without printers may just want to switch the functionality off.

Legally speaking I don't think there's any problem with having an LGPL extension linked from the main program, but it would require a license note stating that the extension was under the LGPL. My main issue with that is that it is a minor pain in the ass. Putting LGPL code in the main program is a no go because that would require relicensing the whole thing to LGPL.