I think the tunnel itself is fine. You’ll be in it a matter of moments, it’s consistent with the look of the area, there aren’t a bunch of conduits on the wall like in the Adventureland tunnel, and assuming the cutouts are windows, you might see a lightcycle woosh by. It makes for a good transition as it opens up to Storybook Circus.
If they were going to expend the effort to do some sort of diorama or show scene, I’d rather they build some sort of trompe l’oeil city of the future on the horizon between TRON and Space Mountain. It would contribute to views from three attractions (railroad, TRON flyover, and PeopleMover) and could potentially be constructed in such a way to at least partially mitigate the look of the adjacent show building from the Contemporary.