Blind Devil already inserted it, so other than some aesthetic changes (like maybe getting rid of the Stone Sea Sanctuary blocks and ruins), it'll remain mostly the same. One notable change however, is replacing Skewer's useless NSMB-esque beach set with the Shemni-Frica Sea tileset, as I did with 1UPdude's level, Tropical Turnout.
Click here to see how it looks thus far. Below is how it looks in-game.
The background is subject to change, but the foreground already looks considerably better with the new set. But, speaking of which...
Okay, that's awesome, I really like the new aesthetic, especially the water.