The Meaning of Life, the Universe, and Everything.
I know it has been suggested before a few times, but I think mine is a bit different. Before I start I dug up some threads of similar suggestions, and a LOT of dynamic water threads, but none had something similar to this (to my knowledge)
TL;dr-Water blocks at layer 64 in ocean or river biomes will spread to adjacent empty blocks
My idea is to "fix" the empty block in the middle of water, caused by placing and breaking (or just breaking) a block in the middle of the surface of a lake, river, etc, which leaves a gap in the surface that isn't a source block. Other examples of how this happens is removing an island, building a bridge and removing it (or a drawbridge), making a boat and then moving it elsewhere via worldedit on server, or making an island smaller.
Now I know you can just place water on the side of a block, or make the water have a block under it, but I thought it would be nice to implement this as an easier, non-processor-eating way, in that all water blocks at layer 64 (sea level) and in an Ocean or River biome (or Lake biome if that is added) would automatically fill any horizontally adjacent air and/or non-source water block with a source water block. This would be toggle-able for the world on creation, and also in server properties, for the sake of mapmakers, and would not be enabled by default on superflat worlds (for seemingly obvious reasons).
While my suggestion adds no additional content, it could be seen as a nice little "bug" fix, even if it wasn't intended as a bug. Thanks for reading!
Edit: While not enabled by default on superflat worlds, it should be able to be enabled, for "fun" purposes