To play a more accurate analogy, it would be as though time itself slowed down when too many people gathered in a city. Unlike the speed of light issue, which we can definitely measure in-universe, such an effect would be as unmeasurable to us as the pathfinding slowdown would be for our simulated dwarves.
Even before I read the second sentence, I was going "well, maybe it
is like that..."
All jokes about life being more leisurely in the country, because they've got plenty of time while the city tries to get things done, if we're being simulated and certain conditions (large groupings of interacting consciousnesses, if that's relevant, but of course I think it'd be more like large groupings of interacting atoms, which make each and every star a computational nightmare on their own) take a lot of Oomph, but the simulation doesn't notice the world. As you say.
The universe could be being 'simulated' by an exact 1:1 scale model of the universe being 'run' (which is a bit arbitrary when it comes to such an extreme) or via a single 'head' Turin machine. Or indeed like
this, which is essentially the same as the latter (and, ultimately, the former).
But if the universe is being strictly simulated in a linear fashion, things can't happen before their causes. This is probably not the reason behind the speed limit of 'c' in such a scenario (which may be a feature of the modelling technique being used, only necessarily a 'bug' by your definition). If the universe is being calculated in a way truly alien to us, perhaps there
is some computational reason behind the old frames-of-reference problem (twins' paradox, etc), but it may be as hard to speculate about that as someone living on a Conway's Game Of Life grid would have in trying understanding a circular ripple. So that way There Be Dragons.
I should be able to mod my dwarves to have [SPEED:-1], which would cause them to appear at their destination before they left.
Um, no. DF works linearly, and while there's no technical reason why Toady could not allow instantaneous travel (one blink, at location A; next blink, at location B... or possibly same blink disappearing from A even while appearing at B) finding an agent at location B prior (even by one blink) even to the
decision to leave location A is not possible, as is.
(If DF were actually to run a multi-pass look-ahead system of calculating movements, covering a 'blink range' sufficient to encompass a given amount of time travel prescience, then it may delay the 'T-zero' blink output until it has worked out T+1 decisions, found out that Dwarf42 wants to have already been somewhere else at T-zero, re-try T-zero with both pre-move and post-move Dwarf42, ensure that the presence of the latter Dwarf42 doesn't change the mind of the former, and then 'release' the T-zero blink in order to re-calcuate for new T-zero (was T+1) and T+1 (was until now the unknown future and still uncalculated). Otherwise, if latter Dwarf42 manages to do something (e.g. pull a level, assuming that this effect were immediate on the accessibility of the faster-than-time path being used[1]) that would have prevented the former Dwarf42 from making that trip, there'd be a "Dwarf42 cancels time-jump: Disturbed by Paradox" or similar, and the T-0 release would occur without such a trip. And you could have a blink range of T0..7 to allow for a series of backwards jumps, but Dwarf42 couldn't actually make more consecutive backwards jumps than the range allows, not without restarting the whole fort from a previous save-point and recalculating, which I'm not sure is what anybody wants. Imagine in a mature fort, Dwarf42, Legendary in every art, craft, skill and martial art there is, making hundreds, thousands or millions of SPEED:-1 steps back in time to be around at the very start of the fort, potentially changing its whole history. Imagine a
Berserk Dwarf42, of the same military prowess, doing the same, and actively wiping it out as a site. Killing himself, his parents or, indeed, his grandparents in the process. Or if not that, at least making a site so different so that there'd be no Dwarf42 the Peasant immigrating shortly thereafter. I don't call it a bug that this cannot happen (although I think it would be interesting if something of a limited nature of this kind could do so, it would have to split 'alternate branches in time', though, if it doesn't do a whole-history recalculation to wipe out paradoxes, or applies a handwavium fudge of some other kind). As such, I don't call it a bug that one cannot call function that in (say) seven iterations of a simple loop cannot find the best (or even a
reasonably best) path between absolutely any point and absolutely any other point. The limitation is informatical, which is not to say that a LogN function might not be available where an N.LogN function is currently used (or whatever the order of overhead actually is). But a bug would be something incorrect, not merely suboptimal.)
TL;DR; - I don't expect to see the Urist McPicard Manoeuvre happening anytime soon.
To be completely honest myself, I tend grow bored of a fort shortly after initial setup; right when I start plotting out the MOST EPIC FORTRESS EVER CONCEIVED™ and remember that building large (complex and therefore interesting) structures is still a PITA, and thus am rarely affected by this myself.
For the last few versions, I've rarely got beyond year 3 or 4, and approaching 100 dwarfs or so (nowhere near the habitually init-revised cap of 300, and 150 kids) before my slow progress (most of the delay is my micromanaging things, although the interminable wait for my the dozen or so Seasonal Saves (my own petard, by which I hoist myself)) gets overtaken by the next version needing trying out (from scratch), or the realisation that I didn't EPIC it enough and wanting to start again... So I know what you mean. Although as the pathing algorithm hasn't significantly changed for quite a long time (and I
do tend to accumulate an awful lot of spare stones, which is part of the original complaint here, IIRC) so I hope you still don't mind me making my own representations on the subject.
[1] Player interaction in-between T0 and T+1 is another issue. In the cached T+1 time-slot, Dwarf42 decides he's jumping back to T0 to craft something, but just as T0 becomes 'real', with Dwarf42 now in both places and T+1/+2 now about to be calculated as the new T0/+1, the player unsets Dwarf42's craftsdwarf assignments. This cannot be applied to pre-jump Dwarf42[2]the only logical situation is that post-jump Dwarf42 finds him or herself having to find something else to do. Regardless, a tachyonic dwarf could not
keep moving backwards in time, and would have to actually bide a wee while awaiting reality to catch them up, at some point. Which sort of puts the mockers down on a SPEED:-1 dwarf or indeed any negative number in there.
[2] Actually, it can in a one-jump scenario, he could just fade out and "has never jumped back, honest guv". But imagine a multi-step jump scenario, which is then allowed to continue for part of that multi- before the correction is made that disperses the possibility of the jump having occurred. You could again Marty McFly him, but it leaves echoes of effect from him having been there and altered others' behaviour. Not that this isn't usable in some way, but it feels very unsatisfactory to me.