My apologies. I was not entirely sober, at the time.
One thing I notice about almost all of your biomes is that we get a strong idea of what the theme is based on the appearance of blocks, enemies, and items, but we are often not treated to a more full-fledged example of what the biome looks like.
If you are into drawing fantasy landscapes, an example background, like those ingame that parallax on the surface or underworld could help. Looking at Terra-Custom shows that many biomes have a number of these backgrounds. Do you have any suggestions, descriptions, or placeholders of what a background for some of these might be?
We also don't know the imagined structures for many of these. For many, a simple world-gen replacer should work. Tropics/tarpit and Jungle/hive could probably use the same world-gen script without too much trouble. Same goes for the marshes/deserts or spider/toad caves, and potentially all aspects of the River/Underworld.
But some of the mini-biomes are much more structured, or are thematically divergent from those they replace. If a simple block-swap was used during world gen to replace living trees with archaic towers, We'd end up with tree shaped stone towers. Are Archaic Towers vertically straight, like the biome signature icon suggests, or are they a bit more fantasy, bending and curving at gentle angles? You suggest that there are 4-5 rooms in each tower, but are they underground or above ground? Are the towers wide, or narrow, with little "wizard-tower" rooms jutting out from the side, with large roofs?
What does a crashed ship look like, and is it roughly the same interior layout as the temple?
Pyramids are largely buried in the desert. Would a necroplis also be mostly buried, with maybe a small mausoleum spire being the surface clue that something exists below? Would the ant-hill replacer use the same world gen "nest" structure for your undead bogs?
Corruption, has a number of roughly vertical chasms, joined by a large horizontal-ish tunnel, while Crimson's world gen places small domed cave mouths on the surface, with a single zigzagging jagged pathway leading to a large, open chamber from which "fingers" jut off protecting the biome's hearts. Infestation is by far my favorite alternate, but what sort of spelunking gameplay does it's world-gen structure provide? I've given it a lot of thought, way more than I should have, perhaps, in lieu of guidance. My favorite concept at the moment, is a sort of gentle, parabolic tunnel generated at the edges of the biome's generated rectangle. like the shape of a bowl. Once you've descended to the bottom of the "bowl," the access into the Infestation's main alien-egg-shaped structure, is actually up, making the exploration of the biome less about falling or navigating downwards, and more about climbing, which can still be challenging pre-hardmode. Whether there's one large, multichambered structure or a number of smaller structures is still something I play with in my mind. Either way, the bowl-with-eggs shape could still be filled in with dirt and stone, leaving plenty of level-ish infested surface. The tunnels could be filled with infested thorns or secreted resin/dried mucus/alien hive-esque stalagmite/ctite unobtainable tiles.