Yeah, pops up now and then, one of the kind souls here (what the heck was their name, can't remember it now) finagled their fix for the graphics handling into toady's hands a while back as I recall, and there are lots of ways which he can theoretically go about multithreading and such but it's one of those things that is a lot easier when you're working from a fresh codebase planned out around such optimizations, rather than trying to port existing stuff to do it. Similar to the 32 bit vs 64 bit stuff, there are methods for these sorts of changes which can be implemented readily in different types of code bases, there are things which might seem obvious to someone who is more of a specialist at programming, and so forth.
As I recall Toady saying, he doesn't see himself as a programmer so much as a game designer (an awesome one, at that) who ended up hacking his way through a jungle of code with a machete he made himself. At this point he's many years along the trail, and some of the suggestions amount to "just rip up the jungle and replant it" though they may seem like "grab a new machete!" at first. I'm no programmer myself, but I have been running exclusively linux, and arch most recently, for years... so there are things I can do, and things I'm comfortable with regarding poking around at bits of code. I myself have gotten a really good grasp of PLAYING df, and am even comfortable with various minor modifications/and such... but just from what I know of how the game operates currently? That's one of those things that we could say, forgo any other features for an arbitrary period of time and hope Toady stumbles on a doable fix before too long... or we can keep playing with the new stuff and hope he stumbles onto said fix along the way, or perhaps someone here finds a way to do it and gets him to implement it.
He added in a lot of stuff with this update, the foundations for lots of cool things, but he's still dealing with a lot of the direct, less directly obvious, and chain-reaction kabooms from this as he goes.
tl;dr, he has plans, I think someone can find one of the listed version goals somewhere that relates to it, but it's a big interlinked problem with no quick fix that we know of yet.