This can already be exploited off the water stream on the magic mapHere are my thoughts on this suggestion. If you were to cover your egg with obsidian, and then to cover it all with water it would take a long time to mine it. But on the positive side of this, it would be very helpful to raid an island, knowing that even if you fall to their island you can place a water bucket below you to save yourself. Either way you look at this there are positives and negatives. So I will give this suggestion a 2.5 cakes out of 5.