There's Unused Space in the Space
The space key takes up the space of ➍ keys but has zero functions except, ugh, space and the language switch button which doesn't seem necessary nowadays when the keyboard works in English just fine (with predictions and all) even with a foreign language keyboard always on.
It's space not very well used, is it not? My proposal is that it would get a new look and new functionality: In lieu of one, we would get four buttons which all still do work as the space button but each of them would get their unique secondary functions. One's function — tongue switch. There rest is up to you. ✌