https://blogs.msdn.microsoft.com/dotnet/2017/10/10/announcin...
If keepass were a .net standard library, you could have different front-ends for various platforms. Making the front-end crossplatform is a good goal too. I'm sure you could use bindings to Qt or gtk. There's various native crossplatform front-ends in the works too. See my comments below.
So .NET Core doesn't benefit from UWP UI library, but UWP typically benefits from .NET Core upgrades.
Looks like Xamarin is building full cross-platform support via XAML
https://blog.xamarin.com/glimpse-future-xamarin-forms-3-0/
Avalonia seems like a straightforward reimplementation of WPF that is already usable.
https://github.com/AvaloniaUI/Avalonia
DotVVM is working on electron support, and I work with it already. I like it.