If all else fails, remember that it will be RNG. You could reroll the world until you get something you like if the editor does not arrive on the first pass.
I already do, I only use advanced world gen, I gen "randomly" until I get a map I like then I abort edit setting and change it so it uses that worlds seed on repeat and then I re-gen until I get a world that has all races and at least one necro tower, I will often gen 10-20 world before actually keeping one.
It's a procedurally generated fantasy world generator. It's entire existence is (will be) geared to ensuring each world is unique. Yeah, you'll be able to limit the creation process a certain way with raws probably, but if you want a world that's fixed in place, you're better off making one with the editor. Well, both will be an option, so it's win-win I guess.
I only use advanced world gen which gives me as much control over the world as I need to create specific world maps/layout and editing the raws allows me control over most of the details of that world, for instance I remove 90% of animal people from the raws, add [max_age] to elves, goblins, dragons ect, remove the [no_eat] from goblins, change it so that it is goblins that eat sapient not elves ect and I do this every single time.
My worlds are not very "unique" at all and I prefer it that way, I love DF not for the random gen but because it takes a simulation based approach to the world and the players place in it, which is why I want as much of the myth/magic stuff to be in the raws as possible because I have the firm belief that if "magic" exists then its "just" another aspect of reality like thermodynamics and it would be used in industry and have fields of expertise based around it.
I don't need (though I wont say no to) a world editor so long as myths and magic are raw editable, like how you could set night creatures/curses to 0 in advanced gen but have them predefined in the raws so that you only ever get were-wolves and never were-tortoises, if magic is raw editable then I could just turn off "procedural" magic and enforce my own predefined magic, I just wish I could turn forgotten beasts off like I do titans.
All of this talking (and thinking) about magic has caused another question to arise for me.
Do you think dynamic combination of magic will be possible with magic, an example being mixing water and fire magic on the fly to create steam or fire and earth to create magma or would such combinations need to be predefined?I'm guessing predefined but can't know for sure.