Nothing game-breaking, nothing astounding. There is a chance I am just being ignorant here or completely missed it in the patch notes, but I thought this was a feature they removed in 1.13... I was playing on a single-player world, and as I tried to place down sugarcane, I clicked the wrong block and placed it under the water, curious to see if it was a one-time bug, I tried placing down more, and all of the sudden I was able to place sugarcane underwater.