Custom selection q

As a player with limited usable vision who has recently started getting into Minecraft, I find it difficult to see which block I have selected. The outline box that is displayed is too thin and blends in with the surrounding terrain. I know there is a mod that allows this, but since I see accessibility becoming a larger focus for the development team, I would love to see this feature brought into the game. I would like to be able to make the box thicker as well as change its opacity and color. Having this feature would go a long way to help me and many others see which block they're about to mine, or determine whether a mob is actually targetted from a distance.