Option in world gen to allow evolution, all creatures start out as a lump of flesh with a brain, mouth, longs, stomach and some sort of mating thing(mitosis as default?), when they mate there is a chance that a tag will be added, modified or removed. This is only during world gen not during the history gen.
Adding and removing any old tag is, well, meaningless. Glance through the CREATURE:DWARF tags and you'll see there's all kinds of tags that don't control anything conceivably genetic, like CRAFTSMAN_NAME, and parametrized tags like SIZE:6 which can't just be changed to a random value.
As Heph noted, in the next version appearance-linked body parts will have associated "genes." That'll be a much more suitable starting point for further implementation of genetics.
World folders: Each world has a folder in which all the RAWs, sites and adventurers etc. folders are in, this allows for seperate Raws for each world but also allows adventurers to visit forts without abondoning as opposed to the current system where both sites AND adventurers use a region folder so you can have only one OR the other.
As Heph said, the next version will copy raws into save folders during world gen. Your visit-without-abandoning thing requires a way to give the AI control of a fortress, which is much more complicated and already has a bunch of Suggestions threads about it.
Didn't Toady always intend for all of the creatures to be procedurally generated? That's why all of the current civilizations are so horribly generic.
He's said he wants procedural generation to have a larger role and the
possibility for it to control everything in non-stock worlds. There'll still be stock world settings with stock creatures though.