Hello,
I already have an UWP custom browser (VS2015, C#) built as interface for controlling an web app, it has common functionalities, but also a lot of custom options that could be used (like user-agent, http headers and so on); it could work with an existing domain or with a locally (embedded) website; the rendered content could be controlled in great extent. The project includes a Microsoft certificate so it's pretty safe to be published no matter how.
This solutions has at least one major advantage against the Microsoft JS/HTML project: it can be compiled to native code.
Regards.