Yeah, CubicChunks was one of the mods listed on the forum post I found, listed as still under development, but it and SpoutCraft requires altering minecraft.jar, which I’m not a big fan of.
But I figured that maybe the developers behind Sponge had included SpoutCraft or a fork thereof. Looked through Ore (World Management), but I couldn’t find any initially, so I’m hoping some users know of some that are compatible with Sponge, if SpoutCraft hasn’t been included in Sponge.