Now that the GMs have officially released
Coastal Sovereignty, I believe that the next obvious step is to allow sovereignty claims on the landlocked bodies of water (i.e. lakes/lochs etc.) This would allow those who are landlocked and/or very far from the freshwater rivers or sea coasts to take advantage of the new technology. The lakes/lochs should be seeded with food using the same matrix as the freshwater rivers or perhaps by using a simple bell curve with a set minimum/maximum amount of food and a random distribution with the majority being in the middle of the curve. Obviously, the same rules on sov and sov buildings would apply to lakes/lochs as with the coastal waters (e.g. you can only build the fishing buildings). It would also mean that the lakes/lochs are no longer just a pretty map feature but rather an additional factor to consider when settling a new city or moving an existing one. It would also help to alleviate some of the overcrowding and land grabbing around the current coasts without, I believe, unduly altering overall game balance and game play.