lemming is building a long stair and you have 5 builders, assign the builder five times to the lemming quickly and fast forward a couple of times, voila! Your long stair is completed! 
Skill queueing like in Lix is a desired feature that I am totally 100% in for!
Lix queuing will affect physics. NL 12.6 requires one frame of shrugging between two builders; player may only re-assign builder during this shrugging frame. Queued builders will skip this frame. Replays with such queuing will fail on NL 12.6. All NL 12.6 replays will play perfectly in (NL with queuing).
Invalid skill assignments that were not wanted before and that are now distrupting solving replays.
First hunch is that this should fail fast and noisily. NL should refuse the replay when opening the file. Nastily, such early detection would require a complete physics simulation; also, viewer would get no information about what the problem is, and would have to guess.
Thus, I have no proposal yet.
I still believe that it is correct for NL to disallow two assignments during same physics update.
-- Simon
Poll