Aerodynamics, probably. Also, at that geometry, if the window were to provide any view forward, it'd need to be enormous.

A full-sized plane would probably have some front-facing windows, but I'd expect most of the visual approach to be done by instruments anyway. In order to have a view of the runway during landing, the Concorde had an enormous and heavy movable nose.

I wouldn't be surprised if it's a thermal issue. Front facing windows on supersonic aircraft get extremely hot. They probably figure they can do better with good camera/video setup instead. Or maybe the pilot wears VR goggles attached to an array of cameras around the plane so he gets a virtual transparent cockpit.

Every image of this plane has a so-called "normal shock inlet," similar to the kind you see on an F-16, for example. These inlets are limited to the low supersonic range. (Mach 1.4 is really pushing it.) So, it's very unlikely that this is a thermal issue, especially given that the F-16 cockpit seems mostly conventional.

Far more likely is that abrupt area changes cause discrete shocks, each of which could merge into the "sonic boom" that the demonstrator is designed to alleviate. However, a simpler way to understand it is that, from a practical point of view, you basically want to be flying a needle to reduce the boom to its minimum possible volume.

> pilot wears VR goggles

I would opt for much simpler camera, an already-proven ILS and windows that allow the pilot to look down on the side of the plane.

The fewer things to go wrong on a brand-new design, the better.

What's the point of X-Planes if you aren't trying out the new toys?

The point is to investigate new airframe technologies, not fully integrated flight systems which the commercial world can handle with DoD contracts.

Also, to properly investigate something, it's usually better to investigate only one thing, not a combination of various different things that,with luck, means something.