Suggestion: Accept double vowels as substitute for kahakō
On a phone it's doable although still frustrating to switch between keyboard layouts all the time, and āēīōū can easily be tapped using Duolingo's own keyboard either way. On a computer, though, it's a lot more annoying to either have to keep moving the mouse and clicking on the letters you need, typing a few more on your keyboard, using the mouse again, and so on, especially in a longer sentence with a lot of long vowels, or to constantly swap your keyboard layout back and forth. I think this could be solved if Duolingo allowed you to enter a double vowel instead of a vowel with a macron, for example, if you could type 'kaakou' instead of 'kākou'.
' is already accepted as a substitute for ʻ because it's a lot easier to type on most keyboards, so my proposal to accept aaeeiioouu as a substitute for āēīōū doesn't sound too outlandish to me. In any case, it would make answering a lot quicker and easier. Finnish users in particular would probably also appreciate this.