Thanks, Fleeting Frames, You're steering me in the right direction.
With the release of the next version tantalizingly close, I've been trying to focus on worldgen tinkering. I apologize for rather ignorant, inattentive, or other missing-the-point questions previously, and I'm not anywhere near the capabilities of the regulars in here. Sedimentary layer generation is still really murky.
I've worked out how to generate large, sprawling rivers with ocean tiles and mountains followed by an elevation gradient, thanks for the pointers on that one! Actually getting sedimentary layers is still hit-or-miss (Clay, shallow metals, and flux stone at least helps narrow things down nicely), though I've definitely grown to appreciate the Region/Biome/Geomanipulator DFhack scripts. That said, I want to not have to rely on hacking scripts for embarks in the future, though "extra-special weird embarks" have produced some very entertaining results. A river source sticking out of the side of a giant "bowl" of elevation, levitating midair brooks (it seems as though DF gives you "the benefit of the doubt" when the only thing tiles connect to are the map boundary, probably the same sort of situation as that fort "nailed to the sky" from a while back), or all layers above the caverns being absent and leading to embarking right on top of a giant mushroom. Among other things. I have also combined regionmanipulator with embark-anywhere to unleash thralling evil clouds straight on top of the elves.
That's all really funny, but I want a worldgen that doesn't rely on external modification (PSVs are still fine) and I can really sink the future (a very long-lived fort with a stable framerate) into. That said, whether or not current worldgens will carry over to the next release very well isn't something I can guess at, though given it's focused on artifacts in particular, it may mostly impact civs rather than geography. I hope.
I've saved all the worldgen params posted in this thread, just in case.
But the ideal for me to work on is:
Embark-level: (at least one site with all of these criteria, though extra potential-sites that only meet some are also hoped for)
A volcano, or magma pipes.
A small aquifer.
Max-openness, single cavern (for FPS sake while still letting fun stuff in once the fort's prepared for it)
Sedimentary layers, preferably well-stocked with magnetite and large amounts of gems.
Any amount of sand, for usage with magma glass furnaces.
Multiple biomes for farming purposes.
So basically, the classic "I want magma forges and tons of sedimentary stone" request.
(An alternative I've considered is to just try and generate as much sedimentary stone layers as possible, then pump magma up, with cavern water sources supplementing.)
World-level:
High counts of vampires to maximize the potential for visitation.
The more necro towers, the better.
Strong titans and megabeasts surviving history generation long enough to have vampires and towers. It takes year 1000 to have full-grown dragons, and this also gives plenty of time for vampires and towers to spread.
Multiple (5+) demons/spires/vaults, but a limitation on "gobsplosion" syndrome, though I have modified raws to partially address this by giving goblins a max age.
On that note, a limit on "elfsplosion" too. I think keeping the civs relatively isolated in corners, as vjek has mentioned doing, is a good way to go about this.
Kobolds that steal from vaults, potentially allowing my fort to procure divine materials by proxy.
I'm not necessarily requesting this, though if someone actually does have a worldgen that crazy specific by all means please share, but that's my goal world to produce.