Forum Moderators: open
So why not have a word-processor application for writing SE-friendly articles? You could set a preference for how often a keyword should appear. The program would then begin highlighting words leading up to when a keyword should come - say five words in different colored type on each side of the "optimal" keyword location.
Icing on the cake would be a final keyword density analysis, and perhaps other similar tools.
Does something like this exist? If not, I'll bet one of the geniuses here could pick up a small chunk of change by building such an application and selling it! ;)