Don't forget, Iceland has a long history of inclusive government and the major literary tradition associated with Scandinavian culture: as a Civ they can wear several hats and not just a Viking helmet.
As for the Ottomans, yes they existed until after WWI (barely) but if the game tends to represent Civs at their Peak, for the Ottomans that was the Exploration Age, at least up to the 1680s (Siege of Vienna). The fact that there's a lot of competition for that Age/geographical spot is, frankly, no different from the Mediterranean Coast/Classical-Antiquity Age, where the game has never had any problem including Rome, Greece, Egypt and (usually) Carthage all at once.
And if the Seljuks/Turkic Khanates are both considered Central Asian Civs, that would lessen the congestion in the middle east considerably: a Central Asian progression of Yamnaya/Scythian/Sarmatian/Xiong-Nu to Seljuk/Sogdian/Gok-Turk/Mongol to Imperial Russia would accomplish that nicely.