Many of the features (Dependency injection, etc) seem only to be available for ASP.Net Core. What about cross platform desktop applications? Do we have a GUI layer that is cross platform as well?
Local files, if you want, make everything lightning fast. Hosting your own web-browser lets you hook into whatever you want, and handle it however you want. A local server makes hosting whatever you want simple, too. There's a pre-existing plugin and component model for serving rich content... Every knows HTML and CSS, and sharding off chunks of the app to a genuine web app is straightforward...
A well factored, MVVM, WPF should be relatively easy to port to this model, and there are mature databinding libraries to handle the plumbing...
Maybe it's just me, but I'd rather take the pain points of a known technology than another 10 years of uncertainty and no cross-platform story.
IP, host header, origin header can be checked as defense in depth, but can't prevent local privilege escalation from non browser clients and are quite fragile even in browsers.
(or use a secure non TCP/IP based communication channel)
That is such a different threat model though. A native app has a lot more permissions than a web page. Trying to protect one native app from another is not really done much. Like, are MS Word documents encrypted so Slack can't read them from disk?
I don't know about the current status of the GUI layer, other than that I've heard plans for WPF to be ported over to .NET Core. I don't know if or when that will actually happen.
They'll still only run on Windows, but it's a nice option for teams that want to move their existing apps over to .NET Core and take advantage of the quicker update cycle and improved performance.