Not anything beta, but I did find two things in Sirena Beach long ago that I never noted on here.

*When you're in the Casino (in Mission 4), there is the (really annoying) game where you have to spray water on these flipping panels to make a shine sprite. Around the game are these rails, that when you completely make the Shine Sprite, go down into the ground. By looking through the wall, you can see the beneath the rails there is a gaint white shape in shape of the rails, and that it never stops falling.

*Also in Delfino Casino, behind everything in the casino, there is a wierd, dark blue texture that I think is also in the Hotel. In one corner of the elevator, the texture is white and goes higher than the rest of the texture for some reason.

None of this is really announcement-worthy, but I am doing some more research of those wierd, unseeable paths that Mario goes in, such as the sewers, and I will make an announcement about that in a few days.