Is it strange that we'd see a glimpse of an announced "future" feature? No. Is it stranger that we'd see a glimpse of an unannounced new track? Yes. But still not exactly strange per se.
PD don't tend to "touch up" their images, although they do tend to turn up the post processing i.e. motion blur, depth of field, antialiasing / supersampling etc. Extra detail in textures is fundamentally different. And there are GT6 watermarks - now, PD are not normally so "dishonest" with their assets.
To me, it screams course maker again - the visibility culling on the Matterhorn tracks was always sub-par, so it would stand to reason that it was a temporary bit of work in lieu of something more dynamic; that being the kind of thing needed for a Ronda-style select-a-course, or indeed, Sierra as a course maker theme. There were always hints of extra layouts for Matterhorn; it could turn out to be an "open configuration", like Ronda was meant to be.
