Not true; if someone writes hundreds or thousands of lines of new code,
    which create additional functionality for something that's under the
    GPL, then there are quite a few limits as to what they can do with
    their code.

This is one of the common misconceptions about the GPL.

This misconception is not new.  I wrote text in version 2 of the GPL
specifically to show it isn't so.

I once asked a person who vehemently condemned the GPL to explain the
reason why.  He said he believed that, if he added a new module to a
GNU program, it would be covered by the GPL by association, and that
he would subsequently be forbidden to use that same module, entirely
his own work, in another program on different terms.

When I showed him the text in the GPL that explicitly says just the
opposite, he changed his mind.