So I have realized, and I am pretty sure this is a bug, but it is possible for rails to be freestanding without having anything under holding it up.

I was playing on my device today, and besides some textures not working for me(probably device problems), I was on a world, and I mined a block from under a rail system, and the rail on that block stayed floating. I know this bug Is for Normal and Powered Rails.
In this screenshot, I do not have Barriers(as they have not been implemented) or invisible bedrock, as it would show the underground caverns. I have not used mods at all on this device or any connecting to this world. I Feel it is a great idea if you fully implement it.