@kehrichtbesen like this idea. More generally (and harder to implement no doubt) would be identifying characters in words that are often confused and boosting those as well. There are many characters and words with very long total practice time that I still get <50% correct, and it’s partly because I’ve never really seen them in context with the ones I’m confusing them with.
From Skritter FAQ, Skritter already spaces out some practice items if they are likely to be too easy because you’ve been practising a similar item recently. If there was some way to do the reverse and reduce the spacing for characters that you’re likely to confuse that would be very helpful.