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About the Netherlands, as the unique leader seems to require R&F (as per the pack #5 description), it implies (at least this is the way I see it) that not only they can be played with a R&F civ, but also there also no civs outside of the R&F expansion that they can lead. If it wasn't so, why specify having the expansion as a requirement? If it was, for example, Kublai Khan, while it's perfectly logical why players without R&F wouldn't be able to play as him leading Mongolia, I see no reason to bar the expansion-less players from playing with him leading China.
Considering how the announcement is phrased, it appears most likely that the new alternate leader will lead only one civ from the R&F expansion and among the possible candidates, Korea and the Netherlands are probably most popular. The inclusion of the latter is further supported by Portugal, whose appearance in NFP seems almost certain. The two civs could be easily thematically paired up with their shared history of trade and colonialism.