Would it be against the GPL to publish a work (eg. a preamble) that has a dependency on both GPL and LPPL packages? The LPPL is not GPL compatible.
Could I argue that the LPPL package is a system library? CTAN actually does specify a list of packages that are required, meaning every latex distribution should have them, so that package writers can require them. At the same time, one problem cannot argue every package on CTAN is a system library.
However the case is much less clear for packages specific XeTeX and LuaTeX. It's unclear when a package is core enough to be a system library, like fontspec or unicode-math. Is there a standard in the community for this kind of thing?
As a followup question, wouldn't this issue result in GPL packages that cannot be modified and redistributed if they use a non-system-library LPPL package?
Please don't talk about the compiled output of the latex document.