1 The current style of maps looks like it wants to copy Apple Maps, but just ends up being worse. There are a lot of great styles by Maptiler/Mapbox that are easier to navigate. For ex., even the "vanilla" Mapbox Standard would work better than the current modified version. All the layers are a bit low resolution as well.
2 Also, from my brief usage, the Wikipedia layer mostly shows battles around the area you're browsing, which isn't super useful when you are looking for map things.

3 My system language is not English, and the UI is weirdly half-English, half-Hungarian
4 A simple link to OpenStreetmap/Tracesmap (or a geo:// shortcut) would be great in addition to Google and Apple
5 Public transport routing with Transitious would be a killer feature, pretty much nobody else offers that reliably outside Google on a generic maps app.
1,2,3 are self-explanatory I think.
4 Would help bridge the gap when you need to look up some detail Kagi Maps doesn't show
5 Would reduce the number of times you have to switch between Kagi Maps ang Google Maps / some other local transit map