I suspect that adding code to the wiki for calculating who's "most responsible" for a good article, so that articles can be voted on for karma (or anything else of this nature that's been suggested) is really tricky. This practically ensures it would never get done, especially since it first requires the account synchronization, which is nontrivial in itself (but worth doing in any case).

I think that the same can be done manually, either by having an actual vote for "Wiki Editor of the Month" or just by announcing completed wiki tasks in a monthly thread and waiting patiently to receive lots of karma votes. Or both, or another similar idea.