A question of curiosity, but what does decide the starting visibility of most civs ? Currently it seems to be linked to... something with varying results, sometimes to extreme degrees. The most obvious one is when playing Norse : there are starts where you have absolutely no sight and you need to pray to Freyr that Dublin has been founded and that the cottages are where you think they are, others where the entirety of Europe, North Africa and the Levant is revealed and you have so much information you cannot really screw up. Surely there could be a middle ground where you get some of the necessary coastlines revealed (the Nord Sea, the Baltic and Europe up until Spain ? Gibraltar ? Rome ? Constantinople if we're feeling really generous ?) while still keeping some of the objectives hidden.
It applies to other civilisations where you are on the clock for conquest or trade : playing Persia with the Levant, Egypt and Anatolia revealed is much more intuitive. The Malay could get a head's up as to which of their key trade partners are still standing. The Tibetans really need to know the state of the basin for these 6 cities, but a full map of Asia indicating exactly where to send the Missionaries makes it trivial.
On an unrelated note, realising that Rome is on the list of possible Norse core targets makes it difficult to ignore. Every time I beeline to it, the city is guarded by practically nothing, it has 1 or 2 Great Generals parked and it's in the perfect position to start further raids and snowball by buying more Huscarls with the plunder. In the usual Civilization scenarios where you play the viking fantasy, getting into the Mediterranean feels like a high-risk high-reward proposition, but here Rome really is the perfect prize for everything — even helping you with the Great Artist depending on the improvements/buildings. Why bother with England or Ruthenia or anywhere with crossbows ? Are the cores of Poland even possible, considering they spawn a few turns before the deadline ?
Maybe the first UHV should be a number/population-size of coastal-outside-the-Scandinavian-and-Baltic + Ruthenian cities instead of a "get cores", so as to keep the "choose-your-own-adventure" of the UHV without giving it a clear answer.