In particular, we'd need a blacklist of libraries to never package.
Um, yeah, some logic needs to be worked out ...
PPM/DEB/RPM... packagers all manage to avoid packing c-runtime... should be able to borrow some ideas/lists from them. On win32 you can filter system dlls by %windir%.
I'd love to have this even just for some platforms, but in a way that doesn't end up with users plastering "PAR is broken on platform X!" all over the internet if this particular bit of functionality is not available for their favourite OS.
I don't see how it can get worse than the current situation.
PAR needs a one-click-checkout, patents be damned :)