Moderator election have a fixed number of free slots, the exact number of slots is determined by SE staff before the election. I'm not sure how they do that, it probably involves reading the entrails of unicorns or something like that.
SE is usually rather conservative in choosing this number in my experience, an that is certainly appropriate considering the amount of trouble and damage a rogue or unqualified moderator could potentially cause. But I also feel that by setting the number low, we often miss the chance to elect some really good candidates on sites that could need a moderator more or two (=Stack Overflow).
So what I want to propose is to allow for more moderators to be chosen in an election as there are official free slots. This already happens if a moderator steps down shortly after an election, but I think a similar mechanism would be useful in other situations as well.
This should still be somewhat democratic, and not solely decided by SE. One option I think would work well would be to put the decision to increase the number of slots when the election is finished to the existing moderators. If the existing moderators unanimously decide that they could need some more help and that the next candidate in line would make for a good moderator, they could vote to increase the available slots.
This would allow SE to continue setting the number of slots at a level where it is very unlikely that unsuitable candidates are elected due to a lack of qualified nominations, but allow the ranks of moderators to be filled more quickly if enough suitable candidates are nominated and voted for.