Hey, the million $ question...
Well, I have removed some starting nations in GC (Pskov, Kurland, Iraq, Tripoli, Knights) and revolter Holstein while I added Montenegro, Mantua, Ryazan and Pomerania as starters. I have also added revolters Serbia, Transylvania, Greece, Finland, Ferrara, Armenia, Novgorod and Antillia (I did not like the New Spain name since, what if it arose out of another State?).
However I would like to bring Pskov and Holstein back for historical reasons and reassert Iraq as a potential rebeller.
I think Pisa, Wales, Flanders, Styria (an autonomous bishopry for a period) and Bremen are defensible choices as would Quebec or some entity in Eastern Canada as a revolter.
Really the new tags would give flexibility without having had to scratch valid original nations. The trade-off would be much less painful since, of the original nations, Kurland and the Knights are really the only two I enjoyed killing off (Kurland cause it never lasted more than 5 years against Poland and its disappearance weakened the Teutons and Prussia too much) and the Kinghts cause they never did anything but sit on their island and send puny ships when their allies declared war.