The show scene directly before the spike is outdoors. So it kind of makes sense not to enclose it. Also, the vehicles are only on the spike for a few seconds anyway. And being able to see a ride vehicle in that section of track from a distance could be a diliberate “weenie” anyways.
I think the fact that the spike appears to have a facade of sorts could be a clue that someone doesn't consider the outdoor spike optimal. Personally, I'm concerned that we'll be able to see backstage from that height, and then you run into the sort of immersion breaking Dragons suffered from, except this time it's on a relatively highly themed ride.