I can't be the only person who's seen the similarities in progression between the two. Craftopia has massive potential in and of itself (if the devs ever finish it), but this game would be an ideal host for a Terraria conversion mod. Map tiles can host 1-2 biomes each. Boss spawns could be tied to item uses, or particular dungeon clears - with dungeons serving as prefabs for stuff like the jungle temple. Asset, animation and effect creation would need to be done from scratch - which, yes, is most of the hard stuff, but would be worth it for the finished product. NPCs are in with the basic functionality needed. Magic's in. Bow/gun combat will likely need an overhaul. Pets/summons are in, if basic.

I'd honestly love to do this myself, but I'm hopeless with programming and don't have the other skillsets necessary to be part of a design team. Failing that, the best I can do is seeding the idea for someone who has the necessary skills to jump on in future. Hopefully in time we'll see something built that makes good use of the best of both games, to create a unique and amazing play experience.